A Numerical Study To Evaluate The Use Of WAG As An EOR Method For Oil Production Improvement At B.Kozluca Field, Turkey

Abstract

Abstract B.Kozluca Field with an OOIP of 138 MMSTB has been producing for more than 16 years. Main producing formation is the carbonate Alt Sinan. Oil gravity is 12.6 °API with a very high viscosity of 500 cp at reservoir conditions. Production mechanism is rock and fluid expansion with a very weak bottom water drive. By the year 2001, the cumulative oil and water production are 3,836,551 stb and 539,059 stb respectively and daily oil production is 570 stb/day with 20 % WC. In 2000, in order to increase the oil recovery, a re-evaluation and reservoir management study was started. This study was initialized by screening the applicable EOR methods. Since there is a CO2 reservoir at Camurlu Field, which is about 10 km from the B.Kozluca field, study was focused on the CO2 injection. Then, a full field simulation and reservoir characterization study was performed. Firstly, a numerical model was used to predict the oil production by current production scenario and then this model was used to make a sensitivity study to determine a certain CO2 injection pattern, number of the injection wells and the optimum injection rate. Although the initial predictions for different immiscible CO2 injection scenarios give very limited incremental oil due to the very adverse mobility ratio between oil and CO2, this application accelerates the oil production. Then, many different Water Alternating Gas (WAG) scenarios were studied and the results showed that WAG will be better than only CO2 injection. In order to find the optimum injection period many scenarios were studied and 60 days of CO2 injection followed by 30 days of water injection scenario was chosen as the best case. Meanwhile, a parallel study was initiated for the design of the surface facilities and well heads for injection wells of B.Kozluca field, a processing facility for CO2 and produced water at B.Kozluca field and CO2 production and treatment facilities at Camurlu field. At the end of the integrated reservoir management study, by applying the WAG technique as an EOR method, it was predicted that more than 7 MMSTB incremental oil will be produced with $ 4.25 MM capital investment for surface facilities, additional perforations, pipe line construction and conversion of production wells to injection wells. With this investment, more than $ 20 MM profit will be gained. Pipeline construction between Camurlu and B.Kozluca field has been already started and Camurlu field surface facilities were evaluated and was found to be sufficient for CO2 production and treatment. Other surface facility constructions are being planned for the coming months. Introduction B.Kozluca Field is located in South East of Turkey, close to Syrian border. The field was discovered in 1985 and was developed with a total of 29 wells. The reservoir has one productive layer, called A.Sinan formation. Since B.Kozluca Field is a heavy oil field, high viscosity and low aquifer support are main constraints for production from B.Kozluca field. The Water Alternating-Gas (WAG) was originally proposed as a method to improve the sweep efficiency of gas injection, mainly by using the water to control the mobility of the displacement and to stabilize the front1. In the recent years, the number of CO2 injection and WAG applications have increased. The main effect of the WAG application is to increase the horizontal and vertical efficiency. The use of WAG strategies has become paramout in the operation and economic maintenance of CO2 floods. It has been found to be an effective and inexpensive tool in the control of gas production throughout the life of the flood2. The main factors affecting the WAG injection process are the reservoir heterogeneity (stratification and anisotropy), rock wettability, fluid properties, miscibility conditions, gas entrapment, injection technique and WAG parameters like cycling frequency, slug size, WAG ratio, injection rate3.