Exercise Contour Maps

(Based on production geology course 2004-2009; Stephan Luthi, Delft University of Technology, and Cees Geel,TNO, the Netherlands)

Hanneke VERWEIJ Email: jmverweij@gmail.com

7-11 January 2013

Sedimentary Basins Formation and evolution of sedimentary basins

& their geo-energy potential

Contour maps

Significance contour maps for (production) geologists and reservoir engineers

Explanation basic contouring principles Exercise

Geology Reservoir Geology Production Geology Reservoir Engineer

Role of Production Geologist Develop Geological Model of the petroleum reservoir(s) Analyze relevant data, integrate them into model Interface with other specialists to provide a Reservoir Model Contribute to and participate in reservoir management A Geological Model is a description of the structure and internal layering of an oil or gas field. It should include a full account of the depositional, diagenetic and tectonic history, and it forms an important part of the Reservoir Characterization process.

Geological model

Correlation

One of the principal goals of the production geologist is to produce volumetric estimates of a reservoir. He/she needs to go through several tasks to achieve this. These include Correlation of reservoir units and their equivalents Producing cross-sections Constructing maps of the top and base of these units Constructing thickness maps Constructing net oil sand maps (All have to be mutually coherent, for which workstations with integrated software are useful)

Contour Map Top Viking Reservoir (Canada)

Cross-Sections and Maps

Cross-sections and maps are among the most important working tools in oil and gas fields. Their preparation was time-consuming when most was done manually, since with every new well required updating them. Computers have largely replaced the manual labor, but the basic concepts remain the same.

Mapping Surfaces

The following surfaces are usually mapped: Structure, usually the top or base of a geological marker,

plotted in contours referenced to mean sea level. The most basic and important map.

Fault Planes, can be contoured if sufficient well or seismic

control exists. Important because of the influence of sealing and throw on the reservoir.

Unconformities and Subcrops, often as contours and as type of subcrops (in color). Important because reservoirs and source rocks often are bounded by unconformities.

Attributes, for example seismic reflectivity, pore type, or facies of a particular horizon. Usually as color maps.

Pressure, as contours at a given time, referenced to a common depth datum across the reservoir.

Surface Contouring

For contouring, interpolation is usually the method of choice, in manual as well as computer-aided contouring. When done manually, one opts for linear interpolation:

Well A

Well B 2760 m ss

2700 m ss

Point where 2750 m ss contour passes through

Well A

Well B

2740 m ss

2700 m ss

Point where 2750 m ss contour passes through

Well C

2760 m ss

Another point where 2750 m ss contour passes through

Local linear segment of 2750 m ss contour

With more wells, the map is divided into triangles and the contour locations are determined in a piece-wise fashion:

The Dipmeter

At this point, the dipmeter needs to be mentioned. This logging tool measures small variations in the resistivities of the rock exposed on the borehole wall with small electrodes in various directions. By cross-correlating them, the dip and azimuth of a layer at a given depth can be calculated.

The Dipmeter For the construction of contour maps, the dipmeter provides a useful measurement, since it indicates the dip and azimuth of a layer of interest in a precise location, namely the well. One way of incorporating this information into map construction is by plotting the azimuth direction as an arrow on the map. The length of the arrow represents the dip, or more precisely, the distance that two contours (at the chosen contouring intervals) are spaced GIVEN THE DIP measured by the dipmeter. In this way, a steep dip results in a short arrow (steep inclines have close contour spacings), while in flatter areas the arrow will be longer. Specifically, the contour spacing CS for a map at scale S is obtained as CS = SCI/tan, where CI is the contour interval and the dip angle.

Dipmeters can be a substantial help in contouring, both for contour direction as well as spacing:

Well A Well B

2740 m ss

2700 m ss

Dip and azimuth in well B

Well C

2760 m ss

Local segment of 2750 m ss contour honoring both well depths and dipmeter data

Dip and azimuth in well C

Surface Contour Map

Ambiguous if only using dipmeter data

Exercise

Figure 1

Figure 2

Exercise Contour MapsContour mapsDiapositiva numero 3Geological modelDiapositiva numero 5Diapositiva numero 6Contour Map Top Viking Reservoir(Canada)Diapositiva numero 8Diapositiva numero 9Diapositiva numero 10Diapositiva numero 11Diapositiva numero 12Diapositiva numero 13Diapositiva numero 14Diapositiva numero 15ExerciseFigure 1Figure 2Diapositiva numero 19