New Steamflooding Techniques Pay Off in Mukhaizna Field
Authors: Feder Judy 
Published: March 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 190478, “Steamflooding Heavy Oil in a Naturally Fractured Carbonate Reservoir in Sultanate of Oman: A Case Study,” by Sanjeev Malik, SPE, Mohammed Al Balushi, SPE, Salim Al Salmi, Aamer Al Belushi, Faris Al Ismali, and Fahad Al Qassabi, Occidental Petroleum, prepared for the 2018 SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 26–28 March. The paper has not been peer reviewed.

An operator has faced a number of challenges producing heavy oil (8000–20 000 cp) from the Khuff and Kahmah carbonate reservoirs at the Mukhaizna field since their discovery in 2010. The large, low-productivity reservoirs have few analogs in the world, so the operator established new approaches to bring these reserves to market. This paper covers the staged field-development methodology, including analysis and evaluation of various development concepts, that enabled the company to optimize both completion design and artificial-lift selection, reducing downtime and lowering operating costs by nearly 50%.

Introduction

The Mukhaizna field, located in the eastern part of central Oman, was discovered in 1975 by Petroleum Development of Oman. The Kahmah Group consists of shelf carbonate deposits of Cretaceous age, whereas the Khuff formation is of Permian age, with a major unconformity between the lower Kahmah and Khuff formations. The lower Kahmah units are believed to have been either eroded away or not deposited in this area. The Mukhaizna field is relatively close to the Huqf axis in southeastern Oman. The Kahmah and Khuff reservoirs are more representative of the interior of Oman than of either northern or southwestern Oman.

The field structure consists of two structural highs, the North structure and the South structure, separated by a saddle in the middle. The first well was drilled in the Khuff reservoir and proved its productivity. Because the shallower Kahmah B reservoir has even more stock-tank original oil in place, the operator decided to assess its productivity while delineating the reservoir by drilling four wells. These wells were drilled in the northern, middle, and southern areas of the North structure in northeast/southwest and east/west directions to acquire information about the fractures throughout the 20,000-acre field. A coring program was initiated at the same time. The results from the wells and cores helped form the Phase 1 field-development plan.

The two reservoirs have different geological properties. Khuff is highly fractured and has low matrix permeability, whereas Kahmah B is less fractured, has higher permeability, and has been dolomitized to varied levels across the field, which has had a significant effect on production performance.

Reservoir-Development Strategy

Steam-enhanced recovery of oil from heavy-oil reservoirs results from reduction in viscosity and residual oil saturation and from distillation. In fractured reservoirs, imbibition may play a significant role in improving recovery. If the crude has more resins and asphaltenes (i.e., more polar compounds), it tends to make the rock more oil-wet. Applying high-temperature steam can alter the wettability, making the rock more water-wet. This helps improve recovery because of imbibition. In addition to the complicated geology of Mukhaizna’s naturally fractured, vuggy, and dolomitized carbonate reservoirs, identifying the right steam-injection method and selecting the best artificial-lift system were critical to the success of the project.