An Integrated Study of Mature Low Permeability Reservoir in Daqing Oil Field, China

Abstract

Abstract Chaoyanggou oilfield is the largest low permeability oilfield of Daqing, and has been under production since 1981. Because of it's complex geological characteristics, significant difference in physical properties of reservoir and crude oil in different blocks, the development effect is not desirable. In this paper, the reasons for the low development effect are analyzed, and the infill drilling is regarded as an effective way to improve the oil recovery and development effect. Through the study, the limit for infill drilling technology was determined, which includes such influential factors as well density, waterflood control degree, low limit of reservoir permeability, and effective displacement coefficient, etc. Also an integrated geological study has been carried out. The primary goal of the study was to develop an integrated reservoir description for targeted infill drilling and improve recovery in a low-permeability reservoir. The field application of infill drilling is very successful and the predicted ultimate oil recovery can be improved by 8.9%OOIP. The study of this low permeability reservoir in the Daqing field is an excellent opportunity to:demonstrate the economic importance of this zones,guide the infill drilling program in other blocks, andhelp the company to find additional reserves in the Songliao Basin. Introduction Since the inception of development of Daqing's Chaoyanggou oilfield, in order to keep the high production rate and oil recovery rate, such strategic development policies as early-stage intensified water injection, high injection-production ratio were adopted. The annual injection-production ratio was enhanced from 2.29 to 3.38, meanwhile, the stimulation measures, like hydraulic fracturing of producers, the change of pumps, etc. were used, but the development effect still was not good, the average oil recovery rate was only 0.7%, the predicted ultimate recovery factor is around 18%OOIP. Aim to the characteristics of low permeability reservoir of Chaoyanggou oilfield, through the analysis, the fundamental reason for the worse development effect is the adaptability of well pattern. Therefore, in this paper, the studies on the reasonable infill drilling method and on economic limit for well pattern infilling were carried out, the calculation method for waterflood recovery factor which is suitable for low permeability reservoir was derived, and also the calculation method for reasonable well density was presented. The infill drilling schemes were designed, and after the field test, a good development effect was obtained, and provide theoretical basis and reference for the development of low permeability oilfield. Geological Characteristics and Reservoir Parameters Chaoyanggou oilfield is located in Songliao Basin's Chaoyanggou terrace of the depressed area and Changchunling anticlinal zone, and is comprised of Chaoyanggou anticline, Fanshentun anticline, Bohetai and Dayushu nose-like structures. Chaoyanggou oilfield is a low and extra-low permeability reservoir in Daqing Oilfield, which is controlled by multiple factors such as fault, structure, and lithology(Deng, et al, 2003). The proved oil-bearing area is 231.1km2, the geological reserve is 16168.2×104t, the average thickness of oil layers is 8.5m. Chaoyanggou oilfield was put into production in 1981. The geologic feature of oilfield is complex, the physical properties of reservoir, properties of crude oil and development of fractures are different in different blocks, and the development effect in various blocks is also different. Development of fractures is different The study on fractures for the early-developed axis area of structure shows that the direction of fractures is mainly east-west, namely, NE85°, the direction is same as the line of injecting wells, the fractures are vertical fractures, and are in shut-in status originally, after fracturing and water injection, the fractures may open and extend. In the following development, it was discovered that the direction of fractures in Fanshentun area is almost south-north.