Qualification and Deployment of a Unique Polymer Conformance Control System
Authors: Beaman Daniel James , Brink David Ian , Ritchie Barry , Pitts Michael John , Jaafar Mohd Rushdan , Abbasy Imran 
Published: May 2016

Short circuiting between producers and injectors continues to challenge operators. A unique water-swelling polymer (WSP) system was developed and extensively tested in the laboratory. This polymer has the ability to absorb 30 to 400 times its weight in water and therefore can plug off high-permeability features or fractures. Because of the size of this material, it cannot penetrate most matrix systems. Another potential application could be the control of lost circulation whilst drilling.

The polymer was benchmarked against various other swelling materials in terms of controllability of swell, long-term resilience to downhole conditions, in particular H2S and CO2, and resistance to acid. The study culminated in a recommendation for trial of this technology in horizontal wells in a water-flood development in the Middle East.

For the trial, an injector-producer, water-flooding pattern was selected that had proven to be ineffective because of a direct connection between the two wells. As a consequence, the injector was taken out of service to sustain production from the producer. This would have been detrimental in the long term, from a recovery standpoint, because of lack of pressure support. As logging or selective placement was not attractive from a risk and cost perspective, a bullhead treatment was the only option to block the high-permeability conduit.

The paper discusses the planning process of this job along with other operational considerations. The pumping was accomplished as per plan and the results proved that the high-permeability conduit had effectively been sealed off. The paper concludes with some learning points and how to expand the scope of this treatment to improve the performance of water-flooding patterns in the presence of fractures.

Introduction

Maersk Oil Qatar is the operator of the Al Shaheen field, which is located on the central axis of the Qatar Arch some 70 kilometers northeast of the Qatar peninsula (Fig. 1). The main targets were comprised of the Lower Cretaceous Kharaib B and Shuaiba carbonate formations, as well as the Nahr Umr sandstone (Fig. 2).

The Kharaib thickness is generally some 80 feet with a reservoir target of some 25 feet. The reservoir comprises tight carbonates with inter- and intra-granular porosity. The Shuaiba thickness is generally some 200 feet thick with a reservoir target of some 20 feet. The reservoir comprises tight carbonates with inter- and intra-granular porosity. The Nahr Umr sand sequence is generally 20 feet thick with targets of some 5 feet of permeable sand. In the reservoirs, the wells are optimally placed in 5 to 10 feet stratigraphic layers.

The field is being developed with long horizontal wells because ofthe large areal extent of the accumulation,poor vertical-well productivity, andthe number of platform locations required if a conventional approach with vertical or slant wells was pursued.

The Al Shaheen development is presently ongoing from nine platform locations, which was only made possible by drilling extended-reach wells.

Wells A (injector) and B (producer) are part of the Kharaib B line-drive pattern to the west of E-location in the aforementioned field. They have been drilled adjacently with an interwell distance of approximately 1,000 ft (Fig. 3). The wells have horizontal displacements along the Kharaib B formation of circa. 18,000 ft. Both are 8 1/2-in. openhole completions. Completion schematics of both wells are shown in Figs. 4 and 5, respectively.

Well B was placed on production in July 2007 and produced dry oil for almost 9 months. In March 2008, a sudden increase in water cut to 36% was observed. This coincided with the startup of injection into Well A, and upon analysis of the bottomhole pressure (BHP), it became evident that the response was directly linked to the water injection into Well A. This interference testing is shown in Fig. 6.