SAGD Trial in Omani Heavy Oil Field Overcomes Suboptimal Conditions

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215943, “Short Spacing, Lower Viscosity, and Suboptimal Operating Conditions SAGD Trial in Mukhaizna Heavy Oil Field,” by Buthaina S. Al Yahmadi, Rawaa M. Al Aamri, and Walaa S. Al Suqri, Oxy, et al. The paper has not been peer reviewed. _ Mukhaizna is a heavy oil field in southern Oman. It is a multistacked reservoir that has been producing under steamflood since 2007. The main sandstone reservoirs were developed using horizontal producers in each target zone supported by vertical injectors. Although most of the patterns are thermally mature, a few areas still are awaiting steamflood response. To mature these areas, a steam-assisted gravity drainage (SAGD) pilot was evaluated, customized, and implemented using existing patterns and well configurations. Mukhaizna Field The Mukhaizna heavy oil field contains viscous, low-gravity (14–18 °API) crude oil in the shallow Permian-age sands of the Gharif formation. Porosity is very good (25–35%), as is permeability (1,000–10,000 md). The Gharif formation consists of upper, middle, and lower reservoirs. Different injector and producer configurations were evaluated to ensure good production. Because a shale barrier clearly was present in the Gharif formation in most of the area but absent elsewhere, the development of this formation was affected. After evaluation of various pattern-configuration options, a development plan was based on three vertical injectors and three horizontal producers per pattern. Thermal development of the field with steam injection began in July 2007. Steamflood maturity has been inconsistent across the field. Various methods of optimizing steam-injection volumes or steam reshuffling in the offset injectors in some patterns were attempted in order to accelerate thermal maturity, but some horizontal producers were still cold with low inflow. To solve this, a pilot-project area with two stacked horizontal producers was evaluated for SAGD potential. These two producers targeted the same zone, Upper Gharif 2A, in one of the best reservoirs in the field. This area was supported by a horizontal injector that had strong communication with the lower producer, but because of misalignment between the horizontal injector and the upper producer, the upper producer was cold, with its progressive cavity pump at pumpoff condition. To evaluate this SAGD trial and predict performance, two analogs were reviewed to compare reservoir properties and parameters. The first analog, Jackfish1, is considered a successful SAGD project, exceeding 90% of its nameplate capacity since first steam. The second analog is Xinjiang oil field, which was not a successful SAGD project, with a steam/oil ratio (SOR) reaching 4.3. This SAGD trial aimed to enhance the oil production of cold patterns with two stacked wells while gaining an understanding of the potential challenges and opportunities of applying SAGD in the existing well configurations at Mukhaizna. The upper horizontal well was converted to a steam injector with an insulated tubing completion. The nearby horizontal injector was kept at the same injection rate to avoid any changes in operating conditions around the SAGD trial.