Petroleum Formation Evaluation -4

7/31/2019 Petroleum Formation Evaluation -4

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PANDIT DEENDAYAL PETROLEUM UNIVERSITYSCHOOL OF PETROLEUM TECHNOLOGY

B.TECH. SEMESTER - VI

ASSIGNMENT - 4

Course: Petroleum Formation evaluation (PE 308)

Problem 1: Using the following figures, estimate GRcorrected under the followingcondition

GRlog reads 67 API units

Hole size = 8 inch

Mud weight = 16 lb/gal

Tool is centered


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Hints: GR logs are subject to a number of perturbing effects including (a) Sonde

position(b) Hole size

(c) Mud weight

(d) Casing size and weight

(e) Cement thickness

Since there are innumerable combinations of hole size, mud weight and tool

position, an arbitrary set of standard conditions is defined in the above figures. A

series of charts is available making the appropriate corrections.

Ans: GRcor = 100


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Problem 2: On the GR log shown on figure below, choose a value for GRmin andGRmax and compute Vsh in sand C using linear correlation between GR response

and Shaliness.

Ans: Vsh = 30%


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Problem 3: In the following example, give most likely cause for the high activityseen on the total GR intensity curve at the point marked A.


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Problem 4:On the log given below, estimate the amount of clay, Vsh, at the following depth:

8,540, 8,549, and 8,560 ft. Do the same using the SP curve and compare. Why

does the SP yield higher values for Vsh in the bottom zone?


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Problem 6:

From the spectral gamma device described above, where the gamma rays from Thand U are predominantly in windows 4 and 5, and where the K gamma ray is

contained only in window 3 and below, determine the response equations for U

and Th. This can be done from a single measurement where the window counting

rates are known, as well as the Th and U concentrations. Suppose window 5 and

window 4 have 40 and 100 counts, respectively, in a formation containing 5 ppm

Th and 20 ppm U.

Problem 7:In the lowest portion (which is water-bearing) of a clean sandstone reservoirknown to be of constant porosity, the density tool reads 2.21 g/cm

3. Further up in

the same reservoir, above the oil-water contact (where the formation is fully

hydrocarbon saturated), the density tool reads 2.04 g/cm3. What is the density of

the hydrocarbon?


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(i) The equation log = 1.0704e 0.188 relates the electron density e tothe tool reading log, which is closely related to the bulk density b. This

equation has been defined so that the tool reading corresponds to b in

water limestone mixtures. What transform would be used for the log

reading to coincide with the bulk density of mixtures of 120 kppm

saltwater and sand (SiO2)?

Problem 8:

The following figure is a short section of the LDT log in the carbonate section of

the simulated reservoir model.

(i) From the knowledge of the density curve alone, what ranges of porositywould you ascribe to the seemingly uniform layer about 12,490 12,540

ft?

(ii) By including the e measurement, could you refine your porosityestimate? What new average value would you estimate it to be?

(iii) What proportion of dolomite and limestone does the matrix seem to be?If not constant, what is the range of mixtures?


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Problem 9:The following figure shows the overlay e versus b for three different matrices as

a function of porosity for lithology determination.

(i) Frequently salt plugging occurs in dolomitic formations whichcontain very saline formation waters. In this case the preexisting

porosity of the dolomite can be replaced with depositions of NaCl.

Plot the trend line on this cross plot for the case of a 20 p.u. water-

filled dolomite in which the porosity progressively becomes salt-

filled. Make use of the mixing law for U.

(ii) From this cross plot alone, with what might you confuse the fullyplugged case?


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Problem 10:

A density log has been run in a sandstone reservoir where core analysis has

determined porosity to be 23%. In this zone the density reading is 2.40 g/cm3.

(i) What do you estimate the grain density of the sandstone to be?(ii) What is the error in porosity if you assume the matrix to be pure

sandstone (SiO2)?

(iii) From the core analysis the formation is known to consist of SiO2 andpyrite (FeS2). What volume fraction of the matrix does the apparent

grain density correspond to?

(iv) The actual grain density from core analysis gives a value of 2.76g/cm3. What does this imply as a value for fl?

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Petroleum Formation Evaluation -4