New Technology Reduces High Water Production in Heavy-Oil Field in Oman

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193658, “Tackling High Water Production in Oman South Fields With New Technology,” by Ayca Sivrikoz, Maria Jimenez Chavez, and Salim Buwaiqi, Petroleum Development Oman, prepared for the 2018 SPE International Heavy Oil Conference and Exhibition, Kuwait City, Kuwait, 10–12 December. The paper has not been peer reviewed. The subject field is one of the largest mature oil accumulations in the South Oman Salt Basin. Production and integrity issues have been challenging in recent years, manifesting in abnormal water cut with time. A multidisciplinary study concluded that this water-cut behavior was the result of naturally occurring fractures that are limited in length and not vertically extensive.• The proposed solutions included detecting fractures early using borehole imaging techniques and using elastomeric zonal isolation packers (EZIPs) in sealing as many fractures as possible. This completion method resulted in delayed water production and increased net present value by $2 to $3 million per•well. Introduction Field N is a complex heavy-oil field in the north of the Sultanate of Oman. It produces heavy oil from more than 1,000 wells, 80% of which are horizontal; all wells penetrate sandstone reservoirs. Production from these reservoirs started from vertical wells in 1985, but the field-development plan recommended a strategy of horizontal wells targeting the topmost part of the sand reservoirs to avoid the predicted oil/water contact to deter possible early water breakthrough. The dynamic behavior of Field N is characterized by strong aquifer and is dominated by bottomwater drive. The study focused on the westernmost accumulation of Field N, called Field NG. From the time Field NG first came on production in 1984 until 2004, the water cut of the field gradually increased to 30% with an average of 20% initial water cut in this 20-year period. However, after 2004, the average initial basic sediment and water (BSW), or water cut, of new wells in the field jumped to 85%, and even wells that started with initially low BSW soon developed a very high water cut in 2–3 months. Through numerical simulation models calibrated with production history from Field N, it was observed that, if matrix conditions are assumed, water is unable to break through immediately at the start of production. Instead, for matrix reservoirs, 1–2 years are required before the water cut can reach 80%. High initial water cuts could only be explained by conductive features such as high-permeability streaks, fractures, and faults. The simulation models investigating the effect of fracture orientation on water development indicated that vertically nonextensive fractures had no influence on water production early on, thus demonstrating matrix-like behavior in the beginning. However, as cones developed and the water table rose with time, water was able to reach these short fractures, and therefore very high initial BSW was observed in new wells. To prove this concept, an extensive literature search—many authors have studied fractures as a possible cause of early water breakthrough—and data-mining study was conducted, which suggested the presence of fractures in the field.