An Energy Efficient Steam Project Through Initial Cold Production and Pressure Depletion in the Mukhaizna Field, Sultanate of Oman.
Authors: Al-Azkawi Ahmed , Koci Paul , Mueller Klaus , Al-Bartamani Nasser , de Bever Frans , Sami Baqi , Francesca Ray , van Den Oord Ruud 
Published: December 2007

The Mukhaizna thermal development is one of the Petroleum Development Oman(PDO) Enhanced Oil Recovery (EOR) projects. On aggregate these EOR projects areintended to move PDO from a current total-concession recovery factor of 12% inyear 2002 to a recovery factor in excess of 50% by 2030. This project is adeparture from the traditional low cost projects in PDO and will require largeannual investments. Cold production from existing wells is expected to reducethe reservoir pressure from 96 bar to less than 40 bar by 2005 to allow energyefficient steam injection. Steamflood development is expected to take place inphases. Phase I, although carrying a strong pilot component, is designed to beeconomic on its own, and is expected to deliver 1600 m3/d hot oil production, starting Q1/2006. The full field development plans encompass drilling andinstalling production facilities to reach a plateau production of 16000 m3/d in2013. Approximately 1200 wells will be required. In the base case a total of 84mln.m3 of oil will be recovered resulting in a recovery factor of 55 % in thesteam developed area.

Introduction

Mukhaizna is the third largest oil field in South Oman, figure 1, it has anexpectation STOIIP of 374 million m3. The field was discovered in 1975 and wasfound to contain heavy, viscous oil (14–16° API, 1500–2000 mPa.s in-situviscosity at a depth of 700mss) in the Upper Gharif Unit 2 (UG2) and the MiddleGharif (MG) reservoir, Figure 2.

The technical difficulties posed by the heavy oil, in combination withrelatively high associated costs, precluded an early development. Economic colddevelopment was made feasible in 1992 by the introduction of horizontal wellsin Mukhaizna.

The development strategy for the field includes an initial conventional"cold" development, which is economically attractive in its own right, and hasthe strategic objective of lowering reservoir pressures sufficiently toimplement an energy-efficient steam injection project. The field was brought onstream in mid-2000 and to date 60 wells have been drilled, of which 51 areproducing. It is producing an average of 2500 m3/d cold oil and approximately2% BS&W.

Geology

Based on Mukhaizna core evaluation and regional knowledge of the Gharif, thereservoirs in the Mukhaizna Field are interpreted as fluvial/alluvial depositsof the Permian age Gharif Formation. The overlying Khuff Red Beds form the topseal for the Mukhaizna Gharif reservoir, figure 3. Productive sands are foundin the UG-2 unit and the upper portion of the MG-R.

The Middle Gharif Shale (MG-S) separating the UG-2 and Middle GharifReservoir (MG-R) is interpreted as floodplain mudstone containing thin, isolated sheetflood sandstones. The thickness and net to gross of the MG-S isvariable across the field, and this may explain why initial reservoir pressureand fluid contacts are similar above and below the shale.

The UG-0 and UG -1 are interpreted as sheetflood and ephemeral channeldeposits. They show some saturation, but are deemed non-producible due toreservoir quality.