Geological Factors in Steam-Soak Projects on The West Side of the San Joaquin Basin

Abstract

More than 10 years' experience in steam-soak operations on the west side of the San Joaquin Basin has disclosed that at least three geological factors are important in such projects. Understanding these factors is necessary for such things as deciding well spacing, selecting the completion zone, and selecting proper completion and workover practices. Introduction There is sometimes a tendency to underestimate the importance of geology in steam-soak projects. Such projects are often carried out in old fields where the limits projects are often carried out in old fields where the limits of the reservoir, the structure, and the correlation, to some degree, have already been resolved by old primary wells. At least this is the case in most of Shell Oil Co.'s steam-soak projects on the west side of the San Joaquin Basin of California. Why, then, do we need to study the geology to convert old wells to steam soak or to infill at closer spacing with soak wells? We cannot use the reasons used for drives of any type where we must assure ourselves through detailed geological studies that the injectors are indeed connected to the producers, for in a soak project the injectors are the producers. After more than 10 years of steam-soak experience on the west side of the San Joaquin Basin, it has been found that several geological factors are important in such projects. An understanding of these factors can aid in deciding on the most efficient well spacing for the project, selecting the completion zone for each well if project, selecting the completion zone for each well if there are several sands present, and determining the length of the interval to be completed if the reservoir is thick enough so that this is a problem. It can also help in predicting how a zone will react to steaming as well as in selecting the proper completion and workover practices. practices.Important geological factors are (1) the environment of deposition - not for that fact in itself, but how that will affect the vertical and lateral transmissibility; (2) the structure and type of trap being dealt with; and (3) the internal features of the rock. To illustrate how knowledge of these geological factors have aided in various steam-soak projects, three different formations that have been steamed are reviewed. The geological factors known about these formations are discussed, as well as how this knowledge has been used in the projects. In order not to be distracted from this purpose, little of the reservoir or production data normally reported for such projects have production data normally reported for such projects have been included. Tulare Sands - West Side, San Joaquin Basin One formation steamed on the west side of the San Joaquin Basin is the Tulare sands of Pleistocene age. Heavy oil shows are reported in almost all the Tulare sands encountered in this area. Attempts to produce these by steam soak have ranged from complete failure to good commercial oil wells. Woodring et al. established that the Tulare sands were nonmarine in origin, having been deposited in and around a large fresh-water lake that covered most of the San Joaquin Valley. Fig. 1 is a map of the different depositional environments that existed around the lake during Tulare time. It is based on paleontological and log studies by Clifford and similar work by the author. As illustrated on the west side, two general environments existed. Farthest to the west and adjacent to the Temblor Range an alluvial plain developed. The Temblor Range was not greatly uplifted, so large alluvial fan deposits like the Kern River series on the east side did not develop. JPT P. 741