Successful Field Pilot of In-Depth Colloidal Dispersion Gel (CDG) Technology in Daqing Oil Field

Abstract

Abstract Based on encouraging results from laboratory studies described in SPE 62610(1), a first large-scale CDG pilot test was started in the largest oil field in China, Daqing Oilfield, in May 1999. The pilot test was conducted in an area of 0.75 Km2, a double five-spot well pattern of 6 injection wells and 12 producers. The well spacing is approximately 250 meters. Up to June 2003, three chemical slugs; 0.179 pore volume (PV) of CDG slug I, followed by 0.155 PV 600 mg/l of polymer solution, and then 0.196 PV of CDG slug II. The drive water has been injected since June 2003. The pilot test indicates that with CDG injection, the reservoir permeability between injectors and producers has been adjusted and volumetric sweep improved. The water cut was reduced by 19.8%, the incremental oil production was up to 24 tons per day in the central production well B1–7-P124 during the peak production period. The pilot test results, to date, demonstrate that CDG technology (1) can be used before, during, or after a polymer flood to effectively control the water production and maintain the high oil rate, (2) has higher incremental oil recovery with better economics than the straight polymer flooding, (3) has wide application in heterogeneous reservoirs for improving water flood efficiency and oil recovery, and (4) can reduce producing water treatment costs as compare with polymer flooding due to lower polymer production in producing wells. This paper describes the reservoir properties in the pilot area, design of the CDG system, injection sequence of chemical systems, injection facilities, monitoring procedures, pilot test performance, and economic analysis. Introduction Mobility control and profile modification are two main methods to improve the sweep efficiency in highly heterogeneous and moderate viscous oil reservoirs. Colloidal Dispersion Gel (CDG), one of several IOR technologies, is designed to improve the volumetric sweep by the in-depth profile modification as well as the mobility control(2,3). Daqing Oilfield and TIORCO Inc. first conducted a joint laboratory study on the use of the CDG process for the Daqing oil field in 1997–98. Then a pilot test was initiated in May 1999. In conjunction with the CDG pilot test, we have also characterized the CDG gellation process, optimized the formulation, and modified the surface injection facilities for the Daqing Oilfield. It was also the first time that CDG was injected alternatively with straight polymer solution successfully. The improvements of permeability variation and sweep efficiency were demonstrated by lower water cut, higher oil rate, and the increase of the total dissolved solids in production wells. During the second stage of low concentration polymer only, water-cut remained low and oil rate remained high for about 8 months but polymer production at the producers increased rapidly. Then the water-cut starts to increase and the oil rate starts to decline. However, water-cut and polymer concentration at the producers again declined and oil rate rebounded after the CDG injection was restarted for the third stage. Current predictions show that the ultimate oil recovery in the central production well will be above 12.0% of the original oil in-place (OOIP) in the central pilot area. The economic analysis showed that the chemical costs were about US$2.86 per barrel of incremental oil recovered. The success of this pilot test opens the door to potential applications of the CDG technology in the giant Daqing Oilfield in China. Pilot Test The pilot area is located in the Northern part of Saertu field and contains six 5-spot patterns with with 6 injectors and 12 producers as shown in Figure 1. There are two central producing wells, B 1–7-P124 and B 1–6-P30 in the test area. The distance between the injectors and producers is approximately 250 meters. The surface area in the test area is 0.75 Km2 and permeability variation is 0.716. The geological description of SII 1–2 sandstone reservoir is given in Table 1.