A Simplified Methodology on Selection, Operation, and Optimum Design of Steam Drive Reservoirs

Abstract

Abstract Steam drive is a viable, proven technology for the development of heavy oil reservoirs. Prior to implementing the steam drive process, a prescreening strategy to evaluate the recovery potential is valuable. Meanwhile, the effect of operating conditions, the design techniques to satisfy specific operating conditions, and the management of any subsequent infill drilling programs in light of the steam drive history are all critical to successful steam drive projects. Based on numerical simulation and field cases, this paper provides some critical strategies and a simplified methodology for evaluating the steam drive process. Based on reservoir physical properties, a pre-screening formula is proposed for computing recovery factors that allow preliminary economic analyses to be performed. It is shown that a successful steam drive project must satisfy the following four operating criteria:Steam injection rate is 1.6 to 1.8 m3/(d.ha.m);Production injection ratio is greater than or equal to 1.2;Bottom hole steam quality is greater than 40% and,Reservoir fluid pressure is maintained below 5 MPa. A design methodology is also provided, which can provide information on the most effective well pattern (5-spot, inverted 7-spot, and inverted 9-spot) and well spacing in order to satisfy the above four criteria. The sensitivity of the methodology to the injectivity/productivity estimates is also discussed. Introduction The steam drive process is an effective technology to develop heavy oil reservoirs. Most steam drive projects operated over the last two decades have achieved satisfactory oil recovery relative to their reservoir properties. From the late 1980s to the early 1990s, more than 10 steam drive pilots were operated in China. Unfortunately, most of them did not achieve their anticipated recovery factors for the following reasons(1):Some key parameters assumed prior to initiating the pilot were not realistic. For example, the steam drive pilot of Du I Group in Du 163 Block applied 5-spot 4 ha well patterns and a steam injection rate of 140 m3/d-CWE. However, the liquid production capacity of a single well was only 40 – 50 m3/d. This low production/injection ratio resulted in poor pilot performance.Some heavy oil reservoirs were simply not suitable for the steam drive process. For example, Well Group 3 –4 –032 and Well Group 3 –4 –76 in Gaosheng oilfield are over 1,600 m deep. At this depth, the bottomhole steam quality remained well below the target of 60% due to excessive heat loss in the injection tubing and the high reservoir pressure.Ineffective operation of the field pilots. The productivity of some pilots was reduced by formation contamination during drilling and completion. In some pilots, the liquid level in production wells was very high indicating poor production optimization and, in most cases, the steam quality was too low to achieve high recovery factors. Based on a theoretical study and field case studies, this paper provides critical suggestions on the following four aspects of the steam drive process:What types of heavy oil reservoirs are suitable for a steam drive project?