While polymer flooding has widely been used as a successful technology to improve mobility control and sweep efficiency in many oil reservoirs, its applicability under harsh temperature/salinity conditions and in low-permeability reservoirs has prohibitively remained a challenge. This study was aimed at investigating the feasibility of low-salinity polymer flooding in a very challenging reservoir located in Kuwait with low permeability (< 10 mD), high temperature (113°C), high salinity (~239,000 ppm), high hardness (~20,000 ppm), and carbonate mineralogy. The evaluation was conducted through a series of systematic laboratory studies including polymer rheology, thermal stability, and transportability using coreflood tests. Our results highlight that the common constraints may be overcome by careful selection of polymer/cosolvent/pre-shearing and appropriate design of low-salinity polymer flooding.

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^

Summary This paper describes recent results from an ongoing geochemical study of the supergiant Greater Burgan field, Kuwait. Oil occurs in a number of vertically separated reservoirs including the Jurassic Marrat reservoir and Cretaceous-Minagish, -Third Burgan, -Fourth Burgan, -Mauddud, and -Wara reservoirs. The Third and Fourth Burgan sands are the most important producing reservoirs. Over 100 oils representing all major producing reservoirs have been analyzed using oil fingerprinting as the principal method, but also supported by gravity, sulfur, and pressure-volume-temperature (PVT) measurements. From a reservoir management perspective, an important feature of the field is the approximately 1,200-ft-long hydrocarbon column which extends across the Burgan and Wara reservoirs. Oil composition varies with depth in this thick oil column. For example, oil gravity varies in a nonlinear fashion from about 10°API near the oil/water contact to about 39°API at the shallowest Wara reservoir. This gravity-depth relationship makes identification of reservoir compartments solely from fluid property data difficult. Including oil geochemistry in the traditional mix of PVT and production logging data improves the understanding of compartmentalization and fluid flow in the reservoir, both in a vertical and lateral sense. The composition of reservoir fluids is controlled by a number of geological and physical processes. We attempted to identify unique sets of geochemical parameters that were sensitive to specific oil alteration processes. One set of geochemical properties correlated strongly with gravity and is, therefore, related to the gravity-segregation process. A second set of parameters showed essentially no correlation with gravity or depth but established unique oil fingerprints for most of the major producing reservoirs and identified a number of different oil groups within the Burgan and Wara reservoirs. We interpret the presence of these oil groups to indicate reservoir compartments owing to laterally continuous shales and faults which act as seals on a geologic time frame. More tentative is the identification of production time frame barriers from the fluid composition data. The oil fingerprint data have been used to distinguish oils from the major producing reservoirs and evaluate hydrocarbon continuity within the reservoirs. Introduction This article describes a geochemical study of oils from the Greater Burgan field, Kuwait. During this study, we examined the compositional variation of oils within the field to evaluate reservoir continuity. This study is part of a larger project to describe the producing characteristics of the major reservoirs in the Burgan field en route to applying the best practices in the overall reservoir management program. In Phase I of this study,1 approximately 60 oils from the Burgan, Magwa, and Ahmadi areas of the Greater Burgan field were analyzed using oil fingerprinting. The objective was to determine if oils from the Wara, Third Burgan, and Fourth Burgan reservoirs had unique oil fingerprints and to evaluate oil mixing because of wellbore communications. In Phase II, a larger suite of wells was sampled to broaden the coverage of the field, both areally and stratigraphically, as shown in Fig. 1. Even though a considerably larger number of wells were sampled in Phase II, the sampling density still remains rather coarse in this supergiant field, spanning 320 sq mile. A variety of different techniques are available for reservoir geochemistry studies.2 The principle method used in this study is whole-oil gas chromatography; sometimes referred to as oil fingerprinting. This method has been described before3 and is, therefore, summarized only briefly here. Oil samples were collected at the wellhead, at atmospheric conditions, and analyzed using capillary gas chromatography. A standard of about 200 calibrated peak heights was developed and from this about 30 standard peak height ratios were calculated. These ratios were selected based on their ability to separate the oils into uniquely different groups. Two different multivariate statistical techniques were used to analyze the chromatography data: cluster analysis and principal components analysis. Both techniques were used to identify groups of similar oils based on the peak height ratios. Petroleum is a very complex natural product whose composition is controlled by various geologic processes which occur both before and after fluid accumulation. In our geochemical studies of the Burgan field, we have used the composition of the produced oil to study the hydrocarbon connectivity of different reservoirs. Some measurements, such as oil gravity, gas/oil ratio and bubblepoint data, characterize the bulk properties of the fluid. Other measurements, such as the hydrocarbon fingerprint, are based on the molecular composition of the fluid. Both types of data are necessary to completely characterize a petroleum reservoir, but the molecular composition data are frequently a more sensitive measure of the reservoir connectivity. Where available, both types of data have been used in this study of the Burgan field. The identification of reservoir compartments, both vertical and lateral, is a necessary component of efficient reservoir appraisal and management. Reservoirs are compartmentalized when barriers to fluid flow are present which prevent fluid communication between different parts of the reservoir. Smalley and Hale have discussed the need for early identification of reservoir compartments well in advance of dynamic production measurements.4 Some barriers are effective on a geologic time scale and frequently result in separate oil pools with unique oil/water contacts and initial pressure gradients. Other barriers may become effective on a production time frame. These are typically identified only after the field is put on production. Reservoir fluid composition data have most frequently been interpreted as indicators of geologic time-frame compartments, but it may provide an early indication of production time-frame compartments in some cases. The Greater Burgan Field The Greater Burgan oil field lies within the Arabian basin in the state of Kuwait. General reviews of the geology and producing history of the field are described by Brennan,5 Kirby et al.,6 and Carman.7 The field is subdivided into the Burgan, Magwa, and Ahmadi sectors based on the presence of three structural domes as shown in Fig. 1. The boundary between the northern Magwa/Ahmadi and the Burgan sectors is the Central Graben fault complex, as shown in Fig. 2.

Summary 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 continuity,identification of production problems caused by leaky tubing strings or leaks behind casing, andallocation of production to individual zones in commingled wells. Results from this study show that while oils from the major reservoir units are different from each other, the differences are small. Furthermore, a number of wells were identified in which mixed oils were produced because of previous mechanical problems. Both transient pressure testing and distributed pressure measurements provided corroborative evidence of some of these findings. Other data show that Third Burgan oils are different in the Burgan and Magwa sectors, suggesting a lack of communication across the central graben fault complex. This finding supports the geologic model for the ongoing reservoir simulation studies. Success of the geochemistry project has spawned enlargement of the study in both size and scope. Introduction This paper describes the results from a joint project by Chevron- Texaco Overseas Petroleum, the Kuwait Oil Co. (KOC), and the Kuwait Inst. for Scientific Research (KISR). Approximately 50 oils were analyzed to assess the feasibility of applying reservoir geochemistry in the Burgan field. All analytical work was performed at KISR. In this study, we report on a subset of these oils that contain primarily single-zone production samples. 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 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 C1-C35+ region rather than the physical properties. Larter and Aplin1 offer a review of many of these methods. 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 enhanced oil recovery (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 (GC). 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 that can be used for correlation purposes.2 This is an inexpensive method and can be very cost-effective when compared to many production-logging methods. Of course, we recommend verifying this technique with other methods before reducing these more costly measurements. A number of papers have documented the application of oil fingerprinting to Middle East oil fields.3–7 Based on these studies, we felt that there was a high probability of success in using reservoir geochemistry in Kuwait's Burgan field. Three applications were of specific importance. Reservoir Continuity. The Burgan field contains several major producing horizons: the Wara, Third Burgan (Upper, Middle, and Lower), and Fourth Burgan reservoirs. Each of these is further subdivided into several reservoir layers. Vertical compartmentalization of the field, both in geologic and production time frames, is possible. In addition, a number of faults have been mapped in the field, and these may act as lateral barriers to fluid flow. The most significant faulting occurs in the central graben fault complex that separates the Burgan and Magwa/Ahmadi sectors of the field. Oil fingerprinting, along with other oilfield data, will be used to evaluate vertical and lateral compartmentalization in the field. Tubing-String Leaks. In many older fields, the integrity of casing strings and cement bonding is often a problem. If multiple pay zones are present, oil may leak into or behind the casing string from zones other than the completion interval. Many wells in the Burgan field produce from two reservoirs. Some wells, for example, produce Wara oil up the annulus and Third Burgan oil up the tubing string. When fingerprints of the individual oil zones have been identified, wellhead samples of the two production streams can be analyzed to determine if a mechanical problem is present.2,8 Production Allocation. It has been shown that the relative proportions of individual oils in an oil mixture can be determined with GC.9,10 Using this method to analyze production streams provides a rapid means of production allocation and does not require that wells be taken off production. In the Burgan field, this method will be applied to evaluate the extent of oil mixing either in the wellbore, owing to mechanical problems, or in the reservoir because of crossflow from deeper, higher-pressure reservoirs. The Burgan Oil Field The Greater Burgan oil field lies within the Arabian basin in the state of Kuwait. General reviews of the geology and producing history of the field are described by Brennan11 and by Kirby et al.12 The field is subdivided into the Burgan, Magwa, and Ahmadi sectors, based on the presence of three structural domes. Fig. 1 shows that the northern Magwa and Ahmadi sectors are separated from the southern Burgan sector by a central graben fault complex.

This paper describes recent results from an ongoing geochemical study of the supergiant Greater Burgan field, Kuwait. Oil occurs in a number of vertically separated reservoirs including the Cretaceous Third Burgan, Fourth Burgan, Mauddud, and Wara. The Third and Fourth Burgan sands are the most important producing reservoirs. Over 100 oils representing all major producing reservoirs have been analyzed using oil fingerprinting as the principal method, but also supported by gravity and sulfur measurements. From a reservoir management perspective, an important feature of the field is the approximately 1,200-ft long hydrocarbon column which extends across the Burgan reservoirs. Oil compositions vary with depth in this thick oil column. For example, oil gravity varies in a nonlinear fashion from about 10 API near the oil-water contact to about 39 API at the shallowest Wara reservoir. This gravity-depth relationship makes identification of reservoir compartments solely from fluid property data difficult. Including oil geochemistry in the traditional mix of PVT and production logging data improves the understanding of compartmentalization and fluid flow in the reservoir, both in a vertical and lateral sense. The composition of reservoir fluids is controlled by a number of geological and physical processes. We attempted to identify unique sets of geochemical parameters that were sensitive to specific oil alteration processes. One set of geochemical properties correlated strongly with gravity and is therefore related to the gravity-segregation process. A second set of parameters showed essentially no correlation with gravity or depth but established unique oil fingerprints for most of the major producing reservoirs and identified a number of different oil groups within the Burgan and Wara reservoirs. We interpret the presence of these oil groups to indicate reservoir compartments owing to laterally continuous shales and faults, which act as seals on a geologic time frame. Compositional differences between groups of oils arise from the reservoir filling process. A third set of parameters correlate with water washing and/or biodegradation processes, indicating oil alteration during production. We are investigating these parameters to determine if they can identify production-time-frame barriers. The geochemical data were integrated with PVT-data for better understanding of the fluid distribution. P. 533