13_PNN_CBM_CaseStudies_ZM

PNN as a tool for coal bed methane (CBM) reservoirs through case studies in China. Author/s: Zoran Markovic, Michail Nicolae

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PNN Annual Conference 2006

“PNN as a tool for coal bed methane (CBM) reservoirs through case studies in China.” Zoran Markovic, Hotwell, Klingenbach, Austria Miichail Adrian Nicolae, Toreador, Romania

Introduction The main component of natural gas is Methane (CH4) the lightest hydrocarbon and that is why it is most closely related in our minds with petroleum industry. But it is the fact that Methane also occurs in association with coal, the World’s most abundant fossil fuel resource. Some conservative estimates suggest that in the conterminous United States more than 700 trillion cubic feet (TCF) of coal-bed methane exists in place, with perhaps 100 TCF economically recoverable with existing technology—the equivalent of about a 5-year supply at present rates of use. Coal bed methane now accounts for about 7.5 percent of total natural gas production in the United States. During the second half of the 1990’s Coal Bed Methane (CBM) production increased dramatically nationwide to represent a significant new source of natural gas. With present situation regarding the hydrocarbon fuel prices it is even more economical to triple efforts on studying and developing coal bed methane reservoirs. Scientific understanding of, and production experience with, coal-bed methane are both in the early learning stages. Much is yet to be learned (1) about the controls on the occurrence and recoverability of coal-bed methane—the geologic, geochemical, engineering, technological, and economic factors, for example—and (2) about the environmental implications of developing the resource. The coal-bed methane industry is still relatively young, and few studies exist of the development and evolution of an individual coal-bed methane play (a group of strata characterized by similar aspects of methane occurrence); thus, few models are available for planning the development of coal-bed methane resources on a broader scale. Studies are now underway and are designed to develop such models and to further our ability to assess accurately the potential coal-bed methane resources. PNN tool is used in old and new wells with primary purpose to provide reservoir monitoring information like present saturation and fluid contacts. This aspect is not in the scope of this paper. Looking for coal bed methane is actually looking for coal beds and PNN tool may have a significant role in looking for coal beds underground by measurement in drilled wells. Measured in cased hole just after casing and after drilling may reduce costs of CBM wells and therefore make CBM production much more economic. PNN tool has several sensors that are measuring and may be used to detect and to evaluate coal beds. PNN measurement was performed on number CBM wells in Alberta, Canada and Montana, USA as well as on number of wells in Chinese coal mines. These measurements were used for building models for coal evaluation using PNN tool. Established models are used for CBM evaluation on number of wells.

What is coal bed methane (CBM)

The primary energy source of natural gas is a substance called methane (CH4). Coal bed methane (CBM) is simply methane found in coal seams or beds and used for a variety of purposes that range from domestic, commercial, industrial to electrical power generation. It has been created during the conversion of plant material to coal, a process known as coalification. Other gases that may exist in coal gas deposits in trace amounts are ethane, propane, butane, carbon dioxide and nitrogen. One cubic foot of methane gas has a heating capacity of approximately 1000 Btu-s (British thermal units.) Natural gas is typically measured in units of one thousand cubic feet (MCF). In the United States, one MCF of methane gas generates enough energy to match the energy consumed by one person for 1.2 days.

It is produced by non-traditional means, and therefore, while it is sold and used the same as traditional natural gas, its production is very different. CBM is generated either from a biological process as a result of microbial action or from a thermal process as a result of increasing heat with


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depth of the coal. Often a coal seam is saturated with water, with methane is held in the coal by water pressure. Currently, natural gas from coal beds accounts for approximately 7% of total natural gas production in the United States.

During coalification, plant material that accumulated in ancient swamps and bogs and was preserved fast enough to prevent decay, begins to compress. This material is first converted to peat as the majority of the water is expelled. As the temperature increases with the continuation of the burial, ranks of coal start to form from this peat starting with lignite coal, followed by subbituminous coal and bituminous coal. Biogenic natural gas (methane attributed to bacterial activity) is first to form. At these different stages of coalification, various hydrocarbons (including coalbed methane), carbon dioxide, nitrogen and water are released. The coalification process can stop at any time, depending on geologic conditions, leaving what we see today as varying ranks of coal. Much of the coalbed natural gas generated by the coalification process escapes to the surface or migrates into an adjacent reservoir or other rocks but a portion is trapped within the coal itself, primarily absorbed on or absorbed within the micropores of the coal.

During the earliest stage of coalification (the process that turns plant detritus into coal), biogenic methane is generated as a by-product of bacterial respiration. Aerobic bacteria (those that use oxygen in respiration) first metabolize any free oxygen left in the plant remains and the surrounding sediments. In fresh water environments, methane production begins immediately after the oxygen is depleted. Species of anaerobic bacteria (those that don’t use oxygen) then reduce carbon dioxide and produce methane through anaerobic respiration. When a coal’s temperature underground reaches about 122 degrees Fahrenheit, and after a sufficient amount of time, most of the biogenic methane has been generated. Also at this time nearly two thirds of the moisture has been expelled and the coal has reached a rank of subbituminous. After the coal’s temperature has exceeded 122 degrees Fahrenheit due to the geothermal gradient and excessive burial, thermogenic processes begin to generate additional carbon dioxide, nitrogen, methane and water. At this point the amount of hydrocarbons or volatile matter has increased and the coal has reached a rank of bituminous (Rightmire, 1984). After the temperature exceeds 210 degrees Fahrenheit carbon dioxide production increases with little production of methane. The thermogenic production of methane does not exceed the production of carbon dioxide in high volatile high ranks of coal until the temperature is about 250 degrees Fahrenheit. The maximum generation of methane in bituminous coals occurs at around 300 degrees Fahrenheit (Rightmire, 1984). During this process large amount of gas is created inside coal – much more then it can hold. Some of this gas escapes into the atmosphere, but some of it remains in the coal. In many areas coal is excellent reservoir for gas (Figure 1). Generally the gas content increases with depth and rank of the coal.

Figure1. Release of gas from coal cleat surfaces.

There were two factors that renewed interest in the financial viability of coalbed natural gas production. First was the development of a production technique in which wells are completed open hole. Second, the use of water well rigs meant that wells could be drilled more economically with a smaller environmental impact as opposed to conventional drilling practices.


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How to find coal bed methane (CBM)

With respect to CBM, it is important to recognize that this resource is directly associated with coal deposits. CBM gas is generated within the coal deposits under both thermogenic (heat-driven) and biogenic (microbe-driven) conditions. At the same time, the methane is trapped in the coal seams by the pressure of groundwater. Releasing the pressure of groundwater from the coal seams liberates the methane that is present, allowing it to be produced as an energy resource. So search for the CBM is search for the coals. Coal Petrophyscal parameters are following: - Low Bulk Density 1.2 - 2.5 g/cm3 - High Neutron Porosity 37 - 60 p.u. - Low Natural Radioactivity - Low Sound Velocity ∆t = 120-160 - Capture Cross Section 13-18 c.u. Coal Petrophyscal parameters detected by PNN tool are: - High Neutron Porosity 37 - 60 p.u. - Low Natural Radioactivity - Capture Cross Section 13-18 c.u. From above list is clear that PNN tool has three sensors that are able to be used for the detection of coal layers. The fact that PNN tool has two neutron detectors makes PNN an excellent tool for the porosity measurement and therefore it is possible to detect coals according to their high neutron porosity. However PNN tool is not compensated neutron measurement and needs to be calibrated in certain conditions. Best is if PNN is calibrated at one well where are available all curves and then this calibration is used at other wells. On Figure 2 there is calibration of PNN porosity curve and compensated neutron porosity curves. It can be noticed that relation is not completely linear and that it deviates in high porosities. Therefore it is necessary to make so called enhancement of porosity curve in higher porosities. After this enhancement PNN curve can completely replace openhole porosity curves. On Figure 3 there is correlation after the enhancement of PNN porosity curve. It clearly shows enhanced PNN curve is completely compatible with openhole neutron porosity curve.


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Figure 2. PNN porosity correlation with Compensated neutron porosity.

Figure 3. PNN enhanced porosity correlation with Compensated neutron porosity.

PNN tool natural gamma ray radiation detector is placed 2.4 m above neutron generator and therefore it s not influenced by radioactivity induced by activation due to high energy neutron bombings. On both figures 2 and 3 it can be seen that coal points are showing low radioactivity.

Coals

Coals


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On crossplot at figure 4 it is better seen.

Figure 4. PNN enhanced porosity vs. PNN GR radioactivity cross-plot.

This cross-plot clearly separates coals from other layers especially non-radioactive clean formations inside measured profile. Although coal in most cases shows very low radioactivity there are some cases when coals are showing high radioactivity. These coals are rare and in most cases are not mature and therefore are not having good gas potential.

Figure 5. PNN enhanced porosity vs. PNN Sigma cross-plot.

CoalsClean sandtones


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Capture cross section of coals is generally low and in range 13-20 sometimes and very rarely it can be higher. So even in the cases when GR and porosity are not enough for determination of coals this third value may help in determining coals. However in perforated coal zones Sigma may be even higher depending on the condition of cement in perforated zone and possible precipitation of high capture cross-section minerals.

By combining all of these three indicators it is possible to evaluate clearly coal layers and also it is possible to speculate about quality of coals. On Figure 5 it is shown one of typical PNN coal detection logs.

Oil Saturation OIl Displ. Water Sat. Shale Sandstone

Coal SaturationCCL 0 5000 GRPNN 30 130

GR OH [GR] 0 150

PNN RAW RATIO [RATPOR1] 0 60

Sw PNN [SWM] 100 0

Sw OH [SW] 100 0

Sigma [SGM] 50 0

Rtio Porosity [RATPOR] 57 7

Porosity [POR] 50 0

PorWaterPNN [PORWM] 50 0

LSN Pnn [LSN] 20 220

SSN Pnn [SSN] 0 1000

PorWaterOH [PORW] 50 0

Lithology [VSH] 0 100

Porosity [PORT] 100 0

1425

1450

1475

Figure 6. Typical PNN coal identification log.


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On the log in first column it is presented GR curve and PNN ratio porosity curves in such scales that are immediately seen separation between two of them in coal zones. Other correlation curves may as well be places here. On next column most important is separation between Sigma and RATPOR curves in coal zones. There is also some other PNN interpretation curves in this column. On third column there are total count rate curves from short and long spaced detectors which show separation between long and short in coal layers. Final column shows lithological analysis if such exists together with volume of coal interpretation.

On this log clearly can be identified two coal layers. The bigger one is at 1567 – 1569 m and thinner one 1435.5 – 1436.5 m. There are probably some more thin layers in zone 1425 – 1445 m. These are very thin and therefore not seen by PNN logs very clearly. PNN tool may confidently detect coal layers of 0.75m and for the ones around half meter they can be notified only.

PNN measurements and case studies in wells drilled in coal mine in China

On selected customers Coal mine with number of drilled wells PNN measurements are made on 4 wells, for the beginning, in order to set the method and to make a proposal how to proceed with PNN measurement in other wells or field with goal to detect gas saturated pockets and by programmed perforation release this gas and therefore reduce mining risks connected with gas fires and explosions.

Like it is already stated customer selected four wells. What were criteria for selection of wells is not known. But some of wells were old and already perforated and some of wells are just drilled and no any operation is done on them. PNN tool is already used in several coal gas fields in Canada with good success in detecting potentially good gas producing zones. Purpose of these wells and PNN measurements was has production and not just release of gas in order to prevent accidents in coalmines. In order to detect coals and gas saturated pockets or layers three types of plots are generated. These three types of plots are present here in order to indicate coal beds and zones, which are gas saturated. All of three of them are presented in order to show to customer in order to define in future which type of processing and which type of plot to produce in order to make good results in coal and gas saturation detection. Log No. 1 This is typical log use for detection of coals and coal gases in nearby sand layers in Canadian coal-gas fields. Log is typically named as Well-1_PNN Processed Log 1_500. Curves presented on Log: Standard PNN Processed Curves Mnemonics RATSNSF Ratio between PNN Short Spacing Detector near and far channels (cps/cps) RATIO Ratio between Short Long Space Detector count rates (cps/cps) SSN Short Spacing Detector count rates (cps) LSN Long Spacing Detector count rates (cps) SIGMA Formation capture cross section (c.u.) CCL Casing collar locator (mV) TOUT Borehole temperature (Deg.C) GRPNN Natural gamma radioactivity (cps) RATPOR PNN Ratio porosity curve calculated by correlation with offset well NPHI curve

or by experience. Also RATPOR1 and RATPOR2 curves. SGM2_12 Sigma from Mode2 Processing between Gates 1 and 2 (c.u.). SGM2_23 Sigma from Mode2 Processing between Gates 2 and 3 (c.u.).


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Sample log of this type is presented through well WELL-1 on Figure on following page. There are several shadings on this log, which are showing either coal beds or possibly gas saturated sands. These are provisory shadings, which may be changed if necessary. On Log are presented several shadings. In first column together with CCL and GRPNN curves are presented RATPOR2 and RATPOR3 curves which are actually copies of RATPOR curve. They are presented in such scales to reflect separation between GRPNN and RATPOR2 (blue) in Coal beds. This separation is presented with following shading:

Separation between GRPNN and curve RATPOR3 is reflecting clean sands and if these sands are higher Gas saturated then separation is higher. This is presented with following shading:


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Separation Potentially Gas Coal

GR from PNN 20 170

CCL from PNN 0 10000

RatPor [RATPOR2]-5 55

RatPor [RATPOR3] 60 0

LSN PNN [LSN] 242 -8

SSN from PNN [SSN] 1000 0

Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0

Temperature [TOUT] 25 30

Ratio [RATSNSF]-36 44

RATPOR [RATPOR1] 60 0

Sigma [SGM2_12] 40 -10

Sigma [SGM2_23] 40 -10

400

425

450

475

500

Figure 7 Standard Coal-Gas detection Log Well WELL-1.


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Since generally coals shows high neutron porosity then there is also shading for very high neutron porosity curve in second column which is also presented with above mentioned Coal shading. There also standard shadings between different curves which indicated in all cases higher possibility for gas saturation. This is presented with following shading:

Separation is made between following curves: LSN – SSN - Short spaced detector and long spaced detector overlay in compatible scales. When this overlay is made and good calibration is made in different zone, gas indication is strictly seen as separation between short and long spaced detector total or partial count rates. In some cases it is necessary to be careful and real tight formations or streaks may show this separation as well. Some local experience should be used in interpretation. RATSNSF – RATIO - Ratio (Short/Long spaced detector partial or total count rates) curve itself is good gas indicator, although sometime can be influenced with gas presence in borehole. RATSNSF Ratio between Short Space Detector near and far channels counts is good gas indicator. On log Ratio and RATSNSF are presented in opposite scales in order to stress gas saturation with shading between RATSNSF and Ratio. SGM2_12 – SGM2_23 - Mode 2 Sigma processing between differtent gates makes good gas saturation indication. These 2 Sigma’s deflects in opposite directions due to different shape of thermal neutron decay (convex or concave) in gas and non-gas saturated formations. 18 – SIGMA - Sigma curve itself is good indicator of gas saturation and on presented processed PNN log there is shading of Sigma curve in zones where Sigma is less than 18. This value is used according to local experience. According to supplied information from local experience generally can be said that if processed Sigma curve is lower than 18 this in most cases means good gas saturation. This should be carefully considered because it may be different for different sands. Generally it can be concluded that if all mentioned indicators are showing good gas saturation then it can be said with high confidence that good gas saturation is present in reservoir.


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Log No. 2 This is typical log used for detection of coals and coal gases in nearby sand layers in Canadian coal-gas fields. Log is typically named as Well-1_PNN Processed Log 1_500_coals. Curves presented on Log: Standard PNN Processed Curves Mnemonics RATSNSF Ratio between PNN Short Spacing Detector near and far channels (cps/cps) RATIO Ratio between Short and Long Space Detector count rates (cps/cps) SSN Short Spacing Detector count rates (cps) LSN Long Spacing Detector count rates (cps) SIGMA Formation capture cross section (c.u.) CCL Casing collar locator (mV) TOUT Borehole temperature (Deg.C) GRPNN Natural gamma radioactivity (cps) RATPOR PNN Ratio porosity curve calculated by correlation with offset well NPHI curve

or by experience. Also RATPOR1 and RATPOR2 curves. Sample log of this type is presented through well WELL-1 on Figure 8 on following page. There are several shadings on this log, which are showing either coal beds or possibly gas saturated sands. These are provisory shadings, which may be changed if necessary. On Log are presented several shadings. First of all higher difference according to Log No.1 is introducing shading between high neutron porosity reading from RATPOR curve and low Sigma readings from Sigma curve. This shading is yet another parameter that shows good separation in coal beds:

There also standard shadings between different curves which indicated in all cases higher possibility for gas saturation. This is presented with following shading:

Explanation is same as per log No 1. Using this log yet another good coal detection method is found. This type of log may be combined with Log No.1 for together presentation on one log.


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Gas Separation

GR from PNN 20 170




Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0



400

425

450

475

500

Figure 7 Log 2 Coal-Gas detection Log Well WELL-1.


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GR from PNN 20 170



RatPor [RATPOR3] 43 -7



Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0



RATPOR [RATPOR] 66 6

Sigma [SGM2_12] 30 -20

Sigma [SGM2_23] 27 -23

400

425

450

475

500

Figure 9 Logs 1 and 2 combined in one Log.


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Log No. 3 On Logs 1 ad 2 only Coal beds are selected and potentially gas saturated zones but this was only qualitative gas saturation. In order to find out how big is gas saturation an quantitative interpretation should be made. Log is typically named as Well-1_PNN Analysis. Curves presented on Log: Standard PNN Analysis Curves Mnemonics SWPNN Water saturation from PNN (%) SW Water saturation from OH if exists (%) SIGMA Formation capture cross section (c.u.) SSN Short Spacing Detector count rates (cps) LSN Long Spacing Detector count rates (cps) POR Effective Porosity (%) PORW Water saturated part of effective porosity OH if exists(%) PORWPNN Water saturated part of effective porosity PNN (%) VSH Volume of Shale (%) VCOAL Volume of Coal (%) PORT Effective Porosity (%) CCL Casing collar locator (mV) TOUT Borehole temperature (Deg.C) GRPNN Natural Gamma radioactivity (cps) Sample log of this type is presented through well WELL-1 on Figure 10 on following page. There are several shadings on this log, which are showing either coal beds or possibly gas saturated sands. These are provisory shadings, which may be changed if necessary. On Log are presented several shadings. Interpreted Coal bed volumes in lithology column are presented through following shading:

There also shadings for interpreted gas saturation. This is presented with following shading:

Other shadings are standard lithology and separation shadings which are similar like in previous explained logs.


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Water Sat. Shale Matrix Gas Sep. Gas

Gas Water Coal Gas

CCL 0 5000 GRPNN 0 200

Temp. [TOUT] 25 30

RatioPorosity 60 0

Sw PNN [SWPNN] 100 0

Sigma [SIGMA] 60 0

Porosity [POR] 50 0

Porosity Wate [PORWPNN] 50 0

LSN Pnn [LSN]-4 246




Porosity Wate [PORW] 100 0

[VCOAL] 100 0

400

425

450

475

500

Figure 10 PNN Analysis Log.


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Input data for interpretation was SIGMA curve, processed from PNN measurement. Parameters for interpretation were obtained from theoretical values and from different cross-plotting techniques. Other input for quantitative interpretation is petrophysical interpretation. Petrophysical interpretation was not supplied by customer and therefore we needed to make petrophysical analysis by ourselves, and this petrophysical interpretation was base for porosity and lithology curves used in quantitative interpretation. Parameters used for this petrophysical interpretation were following. Shaliness calculation – using GRPNN curve. Lithology – As it was information from customer sandstone is lithology model used for this analysis taking into account Coal beds interpretation from previous two logs. Porosity calculation – calculated from PNN ratio curve. It have to be noticed that this porosity interpretation is influenced by gas saturation. So for good porosity interpretation some modelling has to be taken into account. Possible field data for similar reservoirs and possible core data may help to define model for better porosity interpretation in these reservoirs. Ratio curve used for this correlation was curve extracted from Ratio image from Channels 2-18. This is actually closest approximation of extracting curve at end of thermalization process thus gating porosity as much as close to epithermal porosity curve or at time of maximal thermalization. The results from this petrophysical interpretation were used as another input to quantitative interpretation module and are presented together with PNN quantitative interpretation. Parameters for PNN quantitative interpretation used were following and are reflecting theoretical values as well as values got through different cross-plotting techniques. Sigma Matrix value used was 12, for water, 30, and for gas, 7-8. All quantitative interpretation results are presented with Hotwell standard presentation. On figures it is presented Hotwell standard quantitative interpretation presentation where first is depth column with CCL curve, followed with column presenting correlation curves, openhole GR, PNN GR curves and SP if openhole curves are available. In next column is quantitative interpretation of water saturation openhole (if available) and PNN in scale 100 – 0% with red shading for PNN saturation interpretation and blue shading between PNN and OH interpretations. Sigma curve is also presented in this column for comparison. Also when different runs are presented in same log other saturation interpretation curves are also presented and shading between different saturation calculations is present in order to indicate difference. Next column represents total count rate curves plotted in compatible scales in order to show possible gas saturation together with porosity curve and porosity saturated with water curve in scale 50-0 % with corresponding shadings for different fluids. In last column is lithology presentation with porosity. All volumetric curves are in percentages. Complete and all logged intervals are interpreted and presented. These three standard processing and interpretation logs are answering for most of the questions needed to be solved in these kind of reservoirs. Coal beds can be easily recognized as well as potential gas accumulations in porous zones. Quantification of porosity together with saturation can be made and conclusions should be made in order to perforate and release gas from gas saturated zones. Interpretation and Comment for measured wells Comment on processing and interpretation values for all four wells follows. On all four wells coal beds are selected and extracted in these comments. Potentially gas saturated zones are detected and listed with recommendation which zones to perforate.


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Thicker Coal beds are easy recognized, however some thin coal beds of les than 0.6 or 0.5 meters are harder to recognize because of vertical resolution of different logging sensors. PNN tool is good in detecting thin coal beds as thin as 0.5 meters with good confidence. Thinner coal beds may only be indicated by their existence and sometimes are good seen and sometimes not as good. It has to be indicated that by perforation and fracturing of coal beds some pore space may be created and therefore gas may be accumulated in these kind of zones. Well WELL-1 (Figures 7-10) On this well one bigger coal bed can be seen and several thin coal interlayer’s. Thick coal bed 461.8 – 468.2 m Other coal beds are not so visible but according to two types of created logs there are thin coal interlayers on following depths: 503.0 – 504.0 m 494.0 – 495.0 m 479.5 – 480.5 m There are also indications of existence of thin coal layers in following zones: 418.0 – 419.0 m and 412.0 – 415.0 m Just above thick coal bed there is sandstone at 444.0 – 462.0 m. Interval shows strong separation between total count rates and it seems that is partially gas saturated. In some higher porosity zones this intervals shows some gas saturation. By perforation of these zones some gas can be released from these reservoirs. It has to be noticed that gas saturation in this zones is not too high and water production can be expected as well. Even water production may reduce gas production. It would be recommended to perforate most top part of this sand at 444.5 - 447.0 m However when perforated even coal zones (especially if fractured) can produce certain quantities of gas. There are two clean intervals that are showing really high gas indications but these intervals may also be tight zones. Some local experience should be taken into account. If there are no tight streaks in these reservoirs then this two zones are good gas saturated and also my have good gas accumulations. They are at: 477.8 – 479.3 m 492.8 – 493.8 m 502.3 – 502.9 m Well WELL-2(Figures 11-13) On this well one bigger coal bed can be seen and several thin coal interlayer’s. Thick coal bed 431.0 – 438.0 m Other coal beds are not so visible but according to two types of created logs there are thin coal interlayers on following depths:


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450.0 – 451.0 m 462.8 – 463.3 m 419.5 – 420.2 m 362.5 – 363.0 m 355.0 – 356.0 m There are also indications of existence of thin coal layers in following zones: 405.5 – 410.0 m and 381.5 – 383.5 m Few meters above thick coal bed there is sandstone but does not show signs of gas saturation. However when perforated even coal zones (especially if fractured) can produce certain quantities of gas. There are two clean intervals that are showing really high gas indications but these intervals may also be tight zones. Some local experience should be taken into account. If there are no tight streaks in these reservoirs then this two zones are good gas saturated and also my have good gas accumulations. They are at: 448.0 – 450.0 m 461.2 – 462.2 m 502.3 – 502.9 m There is some indication of coal bed at most bottom of logged zone but this is at the end of logged zone. First reading of Short spaced detector is at 471 m. All below is just stanting at bottom of the well.


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GR from PNN 20 170






Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0




Sigma [SGM2_12] 40 -10

Sigma [SGM2_23] 40 -10

350

375

400

425

450

475

Figure 11 Standard Coal-Gas detection Log Well WELL-2.


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Gas Separation

GR from PNN 20 170




Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0



350

375

400

425

450

475

Figure 121 Coal-Gas detection Log Well WELL-2.


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Shale Matrix Gas Sep. Gas Water

Coal Gas

CCL 0 5000 GRPNN 0 200

Temp. [TOUT] 23 29

RatioPorosity 60 0

Sw PNN [SWPNNG] 100 0

Sigma [SIGMA] 60 0

Porosity [POR] 50 0

Porosity Wate [PORWPNNG] 50 0

LSN Pnn [LSN]-8 242




[VCOAL] 100 0

350

375

400

425

450

475

Figure 13 PNN Analysis at well WELL-2.


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Well WELL-3(Figures 14-16) As on the other wells, on this well one bigger coal bed can be seen and several thin coal interlayer’s. Thick coal bed 319.5 – 325.5 m Other coal beds are not so visible but according to two types of created logs there are thin coal interlayers on following depths: 337.8 – 339.0 m 280.0 – 281.0 m There are only slight very weak indications of coals at some other depths: 177.0 – 185.0 m 15 meters above thick coal bed there is sandstone at 287.2 – 302.5 m. Interval shows some separation between total count rates and it seems that is partially gas saturated. In some higher porosity zones this intervals shows some higher gas saturation, especially at top of this sand. By perforation of these zones some gas can be released from these reservoirs. It has to be noticed that gas saturation in this zones is not too high and water production can be expected as well. Even water production may reduce gas production. It would be recommended to perforate most top part of this sand at 287.5 - 290.0 m However when perforated even coal zones (especially if fractured) can produce certain quantities of gas. There is one clean interval that shows really high gas indications but this interval may also be tight zone. Some local experience should be taken into account. If there are no tight streaks in this reservoir then this zone is good gas saturated and also my have good gas accumulations. It is at: 350.0 – 351.5 m


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GR from PNN 0 150


RatPor [RATPOR2]-3 57




Ratio [RAT1218] 40 0

Sigma [SGMAUT] 60 0




Sigma [SGM2_12] 40 -10

Sigma [SGM2_23] 40 -10

175

200

225

250

275

300

325

350

Figure 14 Standard Coal-Gas detection Log Well Well-3.


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Gas Separation

GR from PNN 20 170




Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0



175

200

225

250

275

300

325

350

Figure 15 Coal-Gas detection Log Well Well-3.


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Shale Matrix Gas Sep. Potentially Gas Water

Coal Potentially Gas Coal

CCL 0 5000 GRPNN 0 200

Temp. [TOUT] 21 25

RatioPorosity 60 0


Sigma [SIGMA] 60 0

Porosity [POR] 50 0


LSN Pnn [LSN]-12 238




[VCOAL] 100 0

175

200

225

250

275

300

325

350

Figure 2 PNN Analysis at well Well-3.


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Well Well-4 (Figures 17-19) As on the other wells, on this well one bigger coal bed can be seen and several thin coal interlayer’s. Thick coal bed 272.0 – 279.0 m Other coal beds are not so visible but according to two types of created logs there are thin coal interlayers on following depths: 291.0 – 292.0 m 258.5 – 259.2 m 253.8 – 254.3 m There are only slight very weak indications of thin coal interlayers at some other depths: 175.0 – 185.0 m There are no thick sand intervals in measured zone. However there is a number of thin clean layers and some of them are showing slight gas saturation indications. Best indication is at interval: 288.8 – 291.0 m. Very close to this zone is coal interlayer which possibly supplies gas to this interval. There is also slightly higher indication on zone 240.0 – 241.5 m. On all other zones gas indications are slight. Once again needs to be repeated in such cases saturations with gas need not to be high but gas is still movable.


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GR from PNN 20 170



RatPor [RATPOR3] 52 -8



Ratio [RAT1218] 40 0

Sigma [SGMAUT] 60 0




Sigma [SGM2_12] 40 -10

Sigma [SGM2_23] 43 -7

200

225

250

275

300

Figure 3 Standard Coal-Gas detection Log Well Well-4.


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Gas Separation

GR from PNN 20 170




Ratio [RAT1218] 40 -10

Sigma [SGMAUT] 60 0



175

200

225

250

275

300

Figure 4 Coal-Gas detection Log Well Well-4.


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Shale Matrix Gas Sep. Potentially Gas Water

Coal Potentially Gas Coal

CCL 0 5000 GRPNN 0 200

Temp. [TOUT] 21 25

RatioPorosity 60 0


Sigma [SIGMA] 60 0

Porosity [POR] 50 0


LSN Pnn [LSN]-14 236




[VCOAL] 100 0

200

225

250

275

300

Figure 5 PNN Analysis at well Well-4.


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Summary PNN measurements were performed at four wells from which two were perforated and two are reported not to have perforations. Using described processing and presentation of data it was possible to evaluate coal zones and to indicate some close by gas layers that are possibly supplied by gas from coals. Gas saturation in these layers may not be very high but sometimes even if low these gases are movable. It is necessary to concentrate on these intervals in order to release some gases from mining zones. However gas generation from coals still remains possible and coals if perforated and possibly fractured some pore space is generated and this pore space is supplied by gas from coals and this gas may be produced. This kind of gas production is definitely not very high, but makes lot of problems during mining. In longer term making PNN measurement on several wells and perforating some of zones it would be possibly to model and to differentiate different types of coals with different ability of gas generation. This way perforation procedure may be concentrated on coals with higher gas generation potential.

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13_PNN_CBM_CaseStudies_ZM