Laboratory Studies of In-Depth Colloidal Dispersion Gel Technology for Daqing Oil Field

Abstract

Abstract To investigate the possibility of using in-depth colloidal dispersion gel (CDG) enhanced oil recovery technology for the Daqing Oil Field, a cooperative study conducted by TIORCO, INC., and the Daqing Petroleum Administrative Bureau, was initiated in 1997. The study included a training program to ensure consistent laboratory methods and techniques, tests conducted in both laboratories, and computer simulation. The lab work included screening tests to determine the best polymer and formulation to use for CDG's at Daqing, followed by performance of the optimum CDG formulation in core experiments. Results from the static screening tests and core displacement studies show that the CDG process can further increase the oil recovery over straight polymer flooding and, indeed, is a viable EOR process for the Daqing Oil Field. This paper reports the details of the laboratory studies and initial simulation results which have resulted in plans for a field pilot test. INTRODUCTION The Daqing field is located in Heilongjiang Province, People's Republic of China, in the northeast section of the country. The field is the largest in China, and produces from several distinct layers of sandstone. The degree of heterogeneity varies greatly from one layer to another, and throughout the field. Heterogeneity, combined with mobility ratio, plays a role in limiting oil production on secondary waterflood, causing injected water to bypass recoverable oil. At Daqing, several different improved oil recovery technologies have been implemented to increase oil production, including mobility polymer flooding, surfactant flooding and microbial IOR.1-5 Polymer is manufactured at Daqing and annual polymer injection for mobility control is the highest in the world. Uncrosslinked polymer for mobility control has been effective in increasing oil recovery at Daqing, but straight polymer injection cannot overcome high reservoir heterogeneity, even at high polymer concentrations. Use of polymer gels at Daqing has been limited, but could potentially have a strong impact on future performance of the reservoir. In-depth colloidal dispersion gels (CDG's) correct reservoir permeability variation by causing resistance to flow in the most permeable rock, which forces subsequent injection water into less permeable rock. This results in better sweep of the reservoir and higher oil recovery. Natural reservoir conditions are conducive to CDG injection, placement and performance in ways that are difficult to duplicate in core tests. Injection rates near the injection wellbore are substantially higher than in-situ rates. This allows gelant to move through the sand face without plugging, and to move a substantial distance into the formation, where it is most needed, before "setting up". The reservoir at Daqing has substantial vertical permeability, allowing crossflow between layers. Reservoir rock is typically in a reducing state, which may result in lower adsorption than laboratory tests indicate. This phenomena has been studied and reported for surfactant solutions, but not for polymers or crosslinkers.6 In the lab, these reservoir conditions are difficult to duplicate due to time constraints, distance constraints and equipment logistics. The purpose of the laboratory core tests was to demonstrate the enhanced properties of CDG's relative to uncrosslinked polymer, that result in improved oil recovery in heterogeneous rock. Efforts were made to design core tests carefully in order to account for natural reservoir conditions, while accounting for the constraints inherent with core testing. The specific goals of the core work were to obtain the best verification possible that:CDG's propagate in cores and have similar injectivity to uncrosslinked polymer.CDG's increase resistance factors in cores substantially over uncrosslinked polymer.CDG's are still capable of forming gel after moving through porous rock.