Achieving Solids-Free Gas-Production Target Rate From Highly-Unconsolidated-Sandstone Formation Intervals
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 141878, ’Achieving Target Solids-Free Gas Rate From Highly- Unconsolidated-Sandstone Formation Intervals,’ by Nahr Abulhamayel, J. Ricardo Solares, SPE, Walter Nunez, Ataur Malik, SPE, Mustafa Basri, SPE, and Andrew McWilliams, Saudi Aramco, and Oumer Tahir, SPE, and Mohammad Abduldayem, SPE, Weatherford, prepared for the 2011 SPE Middle East Oil and Gas Show and Conference, Manama, Bahrain, 20-23 March. The paper has not been peer reviewed.

One of the most challenging aspects of producing wells drilled in the unconsolidated pre-Khuff gas reservoirs in Saudi Arabia is to achieve solids-free production while trying to achieve high gas rates. Challenging reservoir conditions include high temperature and pressure, high stress, heterogeneity, and the absence of stress barriers that together make placing fracture treatments very difficult. Stand-alone screens were installed in openhole well completions in the sandstone reservoir and achieved excellent results by eliminating the need for a fracturing treatment.  

Introduction

Achieving solids-free production from unconsolidated-sandstone reservoirs is an ongoing challenge. The importance of effective sand control in these wells is the need to maintain the integrity of bottomhole and surface processing equipment and facilities, and to ensure that production targets are met consistently. Fig. 1 shows examples of the potential damage that sand production can cause.

Several approaches including indirect hydraulic-fracturing stimulation, high-angle and increased-contact wells, and, more recently, sand-screen completions have been used to develop these gas reserves. Among these approaches, the sand-screen completions, in both vertical and high-angle wells, was field tested in two wells, and then it was implemented in more wells after the success of the pilot.

Formation Geology

The sandstone formation in which the two well pilot tests were conducted is a siliciclastic formation in the pre-Khuff stratigraphic section in Saudi Arabia. Gas resources are in sandstones of variable quality within a sequence of sandstones, siltstones, mudstones, and shales. Because the formation was deposited in a shallow marine tidally influenced shoreline setting, it is heterogeneous in character.

Heterogeneity imposes both vertical- and lateral-distribution variability of reservoir-quality properties over a wide range of scale and geometry. Reservoir quality in this sandstone formation is a function of several factors, particularly grain size and sorting and clay type and content, which are controlled largely by the primary sedimentological process. Sandstone cementation and diagenesis-controlled cementation also play a role. These reservoir-quality-influencing factors are, in turn, subject to sedimentological and diagenetic processes, controlled largely by the depositional setting. Porosity and permeability of the gas-bearing intervals vary over a wide range. The well-plan metric for the initial gas-production rate from the formation is from 15 to 20 MMscf/D. Although this rate is achievable, given the permeability and pressure characteristics of the reservoir, the formation’s unconsolidated nature increases the risk of exposing equipment to damaging sand production.