The Impact of Pressure Drop on SAGD Process Performance

Abstract

Abstract Pressure drop along the horizontal wells and between the injector and producer could have a significant impact on SAGD process performance. However, this issue is poorly understood due to difficulties in simulating pressure drop. This paper presents the results of a numerical study on the topic. When pressure drop between the injector and producer exists, the downhole vapour production rate must be increased significantly. Without adequate vapour production, the oil production rate is lower and SOR is higher. Increasing the vapour production rate may affect pad facility design as more vapour handling capacity is required under these conditions. On the other hand, pressure drop inside the injection well may also alter steam distribution. However, the impact on oil production is limited as steam can move relatively easily inside the steam chamber. In the present case, oil production is reduced by approximately 5% when a pressure gradient along the injection well is considered. Introduction Steam-Assisted Gravity Drainage (SAGD), a thermal process that involves the application of steam and the use of horizontal wells, is a bitumen recovery method used in the Athabasca Oil Sands. The most common implementation involves the use of two horizontal wells drilled parallel to one another with a vertical separation distance of about 5 m. The upper well is known as the injector and the lower well is known as the producer. Through the operation of commercial projects, it has been observed that once steam is injected into the reservoir, a pressure gradient is observed along and between the wells. There have been a number of publications addressing this issue(1, 2). As the SAGD process has been applied to more locations in recent years, considerable interest has been generated around the topic of pressure drop and its effect on SAGD process performance. It is generally understood that a pressure drop across or along the wellbore could result in wells with a non-uniform steam chamber, a reduced effective wellbore length, liquid build-up above the production well or reduced oil production rate.* When a new reservoir is developed, a great effort is required to understand the reservoir characteristics and how to incorporate them into production forecasting models. Petro-Canada is currently expanding their MacKay River project and, in order to develop a better understanding between pressure drop and oil productivity, the field data from their existing project was analyzed so that recommendations could be made to increase the project's productivity. One factor that needs to be addressed for drilling and completion planning is the wellbore size. Larger wellbore size results in more uniform steam distribution in the injection well and increased productivity from the production well. However, a larger wellbore size incurs a higher cost. In some existing wells, it was found that liquid build-up was occurring due to limited lifting capacity. In addition, a larger pressure drop between the injector and the producer has been observed.