Application of Novel Technologies Helps Unlock Deep Omani Gas
Authors: Wilson Adam 
Published: February 2015

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 152436, ’Application of Novel Technologies Helps Unlock Deep Omani Gas,’ by Andreas Briner, SPE, Joe Curtino, and Hisham Al-Siyabi, Petroleum Development Oman, and Tobias Judd, SPE, Schlumberger, prepared for the 2012 SPE Middle East Unconventional Gas Conference and Exhibition, Abu Dhabi, 23-25 January. The paper has not been peer reviewed.

With unique geomechanical, reservoir, and geological properties, some of the large gas-bearing prospects within the Fahud basin in the Sultanate of Oman require innovative drilling and completion practices. A revised drilling and completion workflow, with specific technology deployment and operational flexibility, has been developed in order to account for such reservoir complexity.

Introduction

Early Paleozoic nonassociated-gas fields operated by Petroleum Development Oman in Oman have traditionally comprised good-reservoir-quality sand-stones located on three- or four-way dip-closed structural highs. While gas-exploration success has continued since 2005, discoveries have been restricted to much poorer reservoirs.

Successful continued exploration, appraisal, and further maturation, especially as exploration is also extended into basin-center locations, pose significant challenges given the depth (high temperature and high potential reservoir pressures) and reservoir quality [porosities ranging from less than 3% to 10%, with (ambient) permeabilities ranging from 0.001 to 1 md].

Following a successful completion of a regional basin-evolution and burial history study, a well campaign mainly targeting the Amin-Nimr section in the Fahud Salt basin was designed. The target reservoirs of the Amin formation and Nimr group are Cambro-Ordovician in age and are separated by the Angudan unconformity, estimated to represent a hiatus of up to 20 million years.

The Amin and Nimr units are both recognized in the sedimentary basins of north and south Oman, but they have widely differing properties. The Amin formation is a high-net-to-gross-ratio, continental succession deposited in alluvial-/fluvial-fan, sabkha (wet and dry), aeolian, and fluvial sheetflood/sand flat environments, generally with a high water table. The underlying Nimr group comprises two formations, a unit comprising fluvial and lacustrine/playa deposits overlain by a unit comprising large-scale coarsening-upward fluvial deposits.

New Operating Model

Past reservoir-characterization methods are no longer sufficient when appraising low-permeability gas reservoirs where performance is directly linked to reservoir quality and the effectiveness of the selected method of reservoir stimulation.

Several technologies have been applied recently in Oman to improve the understanding of tight gas opportunities, and these include the incorporation of advanced drilling practices; improved understanding of subsurface environment and hydraulic-fracturing design and methodology; hydraulic-fracturing evaluation; and well-completion considerations from a hydraulic-fracturing and subsequent-well-production standpoint.