Paper: Application Of Geological Isometric Cross-Sections To Secondary Recovery Projects

Major assets of producing companies include reservoirs that are subject to secondary recovery operations. These secondary projects can be improved upon through the proper application of technical knowledge and experience. During the past 10 years, large investments have been made in initiating new water-floods and gas injection projects. Improved recovery programs have been undertaken in existing secondary operations which include infill drilling, converting new or existing wells to injection service, and well workovers designed to control or improve injection profiles. With all this activity there is a definite need to monitor well and field performance to maximize both profit and recoverable hydrocarbon reserves. Today, high pressure waterflooding is relatively common. Typically, injection may exceed reservoir voidage over a prolonged period of time and even after fillup of the free gas space. Under such conditions, it is advantageous that everything possible be done to maximize oil production. Isometric diagrams and calculations can be used to pin-point candidates for large volume lift, selective well completions, and additional infill or development drilling since increased withdrawals a.re often indicated to prevent reservoir pressure from increasing unnecessarily. The use of geological isometric cross-sections in studying and monitoring secondary-recovery programs has wide application. The isometric crosssection provides a means of incorporating inherent geological parameters that materially affect all injection projects. Of primary importance is the geological interpretation presented on the isometric cross-section showing the continuity of the various layers which directly affects vertical and horizontal sweep efficiency in a secondary-recovery project. Since the unit displacement efficiency is fixed by the injection fluid selected, improvements in existing secondary-recovery projects require a better understanding and application of geological interpretive knowledge to develop practical means of improving the area1 and vertical sweep efficiency of each pattern or tract. During primary production operations, only limited geological information is required after development drilling operations are concluded. For example, isometric cross-sections could help in primary well completions. It is only during secondary recovery operations that a more detailed and reliable geological description of the reservoir is required for monitoring the progress of the flood throughout the reservoir. The need for geological definition may become quite apparent when secondary flood performance differs substantially from predictions and forecasts. Another basic use of geological data is in properly modeling the effects of stratification. This procedure is necessary in order to match reservoir performance history in reservoir simulation studies and make reliable predictions of future performance. Exotic or tertiary recovery programs will have to be selected by operators who have the necessary technology, including a better understanding of the inherent heterogeneous nature of reservoir rocks.