Practical Experiences of Improvement Oil Recovery for Weizhou 11-4 Bottom Water Oilfield in South China Sea

Abstract

Abstract The Weizhou 11-4 oilfield is located in the North Gulf Basin of South China Sea. This oilfield is the massive sandstone reservoir of marine sedimental formation with strong bottom water drive. Its structure is a simple and complete drape anticline without faults. The reservoir geological properties are fairly good. The average porosity is 22%, and the average permeability is 945md. The thickness of sand body is from 30m to 50m. There is a stable distribution of the tight sandstone layer to be developed just above the oil-water contact in the entire oil-bearing area. During the oil producing period, the operator had emphasized on the combination research of fine reservoir description and reservoir simulation. So the production performance of the oilfield was improved significantly. The original oil in place (OOIP) has been greatly increased from ODP's 1817×104 m3 to updated 2550×104 m3 by the integrated reservoir characterization. The incremental OOIP is about 733×104 m3. By the end of 2001, the cumulative oil production is up to 824.47×104 m3 of which it is about 32.3% OOIP and water-cut is about 71.1%. According to the results newly forecasted, the ultimate cumulative oil production can be up to 1096×104 m3. The 725×104 m3 of incremental oil recoverable reserves has been enhanced than ODP's 371×104 m3, and its oil recovery factor has been improved from ODP's 20.4% OOIP to more than 42.98% OOIP. Based on more than eight years producing experience of this oilfield, although it is marginal originally, great development effects and economic benefits have been achieved by using effective stimulation measures, such as drilling multilateral or single horizontal sidetrack wells, drilling additional wells, enlarging draw down pressure, enhancing the liquid production rate especially in the middle water cut period. All these stimulation measures have effectively increased the sweep efficiency, extended the period of production plateau, ensured the average yearly oil production to be more than 4% OOIP lasting out eight years, and also improved the oil recovery. This paper, from the point of view of oil field development and reservoir management, presents the main development strategy and technical experience of this oilfield based on its general situation, geological characteristics and production performance.