Characterizing the Greater Burgan Field: Use of Geochemistry and Oil Fingerprinting

Abstract

Abstract This study reports reservoir geochemistry findings on the Greater Burgan field by a multidisciplinary, multiorganizational team. The major objectives were to determine if unique oil fingerprints could be identified for the major producing reservoirs and if oil fingerprinting could be used to identify wells with mixed production because of wellbore mechanical problems. Three potential reservoir geochemistry applications in the Burgan field are:evaluation of vertical and lateral hydrocarbon continuityidentification of production problems due to leaky tubing strings or leaks behind casing andallocation of production to individual zones in commingled wells. The latter two applications are especially important in many older fields, such as Burgan, where tubing and casing string leaks are a problem. For example, Burgan wells which produce Wara oil up the casing and Third Burgan oil up the tubing need to be monitored for the occurrence of mechanical problems. In this case, the chromatography method adds value by reducing the number of high-cost production logging runs and eliminating the associated lost production. Results from this study showed that oils from the major reservoir units are different from each other, even though the differences are small. Furthermore, a number of wells were identified where mixed oils were being produced because of previous mechanical problems. Both transient pressure testing and distributed pressure measurements provided corroborative evidence of some of these findings. Other data showed that Third Burgan oils were different in the Burgan and Magwa sectors, suggesting a lack of communication across the central graben fault complex. This finding supported the geologic model for the ongoing reservoir simulation studies. Success of the geochemistry project has spawned enlargement of the study, both in terms of size and scope. Introduction This paper describes the results from a joint project by Chevron Overseas Petroleum, the Kuwait Oil Company (KOC) and the Kuwait Institute for Scientific Research (KISR). About 50 oils were analyzed to assess the feasibility of applying reservoir geochemisty in the Burgan field. All analytical work was performed at KISR. Reservoir geochemistry involves the study of reservoir fluids (oil, gas and water) to determine reservoir properties and to understand the filling history of the field. Many of the established methods for exploration geochemistry can be used for this purpose. Reservoir geochemistry differs from other reservoir characterization methods by dealing primarily with the detailed molecular properties of the fluids in the C, -C35+ region rather than physical properties. A review of many of these methods can be found in Larter. Geochemistry techniques have been used to help solve reservoir problems for many years. During this time, oil geochemistry has been applied to the following reservoir characterization and management problems:–Evaluation of hydrocarbon continuity–Analysis of commingled oils for production allocation–Identification of wellbore mechanical problems–Evaluation of workovers–Production monitoring for EOR–Identification of reservoir fluid type from rock extracts–Characterization of reservoir bitumens and tar mats Many different analytical techniques have been used in these reservoir geochemistry studies. One of the most widely used is gas chromatography. When used for oil correlation it is often referred to as oil fingerprinting. In most reservoirs, the oil composition represents a unique fingerprint of the oil, which can be used for correlation purposes. This is an inexpensive method and can be very cost effective when compared to many production logging methods. P. 385^