Offshore Water-Disposal Wells: Formation Damage and Treatment

This article, written by Dennis Denney, contains highlights of paper IPTC 16595, "Formation Damage and Treatment of Offshore Water-Disposal Wells in Saudi Arabia: Case Studies," by Ken Mei, Hassan B. Qahtani, Abdulmohsen S. Al-Kuait, and Luai A. Sukkar, Saudi Aramco, prepared for the 2013 International Petroleum Technology Conference, Beijing, 26-28 March. The paper has not been peer reviewed.

In one Saudi Aramco offshore oil field, the production from different platforms is transported to an onshore gas/oil-separation plant (GOSP) where the produced water is removed from the hydrocarbon stream. Then, the produced water is injected continuously into highly permeable formations through disposal wells. Therefore, the water-disposal system is an integral part of the hydrocarbon-recovery system. Failure of one of the disposal wells could affect oil production adversely.

Introduction

Field A is a mature oil field with more than 500 active producing wells, and it has been on stream for more than 50 years. The crude-oil-handling facility was built onshore with limited equipment capacity and a limited water-disposal capacity. The field produced formation water beginning in the 1980s, and the water cut has increased over time. This field is expected to continue operating at approximately full crude-oil-handling capacity, with all produced water to be dis-posed of continuously. The main focus is how to maintain the ability to dispose of all the produced water.

Of the options studied, the best was to drill new water-disposal wells and to service existing disposal wells to maintain a high disposal capacity. Evaluation of the disposal capacity of each well is the core part of this option and is a major challenge associated with a water-disposal system. Well tests on water-disposal wells are uneconomical to conduct monthly. Also, water injection would have to be interrupted during testing.

Another major challenge was determining an effective treatment for water-disposal wells that have encountered a significant drop in injection potential. The produced water contains a significant amount of waste material including solids, salts, chemicals, and residual oil. Even after being treated, the waste-water causes pipeline corrosion and formation damage. Conventional acidizing with hydrochloric acid (HCl) or mud acid (12% HCl+6% hydrofluoric acid) proved ineffective for treating the formation damage to improve injectivity. A new way was found for dealing effectively with injection loss caused by specific formation damage.

Water-Disposal System

The produced water passes through high- and low-pressure separators and then is pumped to the disposal wells by two injection pumps and a 24-in. above-ground pipeline. Because the water-disposal system is part of the hydrocarbon-recovery system, reduction of produced-water injection would restrict oil production. An increasing number of wells have electrical submersible pumps (ESPs) installed to produce fluid at higher rates, which accelerates water production. With new ESP wells coming on stream, in a few years the water volume will be two and one-half times the current produced-water volume.