The Environmental Benefits of Reducing Unwanted Water Production

Abstract

Proposal The Gulf of Thailand (GOT) has been producing oil and gas for approximately twenty four years and, at present, water production is becoming a serious dilemma for some operators.Because most of the production from the GOT is from co-mingled monobores, having multiple pay sands of highly variable permeability and natural fractures, the risk of early water production is high.Unwanted water production in Thailand has resulted in many of the classic negative effects such as, water "loading", causing lost production and reserves, bottlenecking surface facilities and increased operating costs, due to water handling. Because tourism and fishing are critical to Thailand, the environmental impact of produced water is also a major concern.Several initiatives have been undertaken to address the issue of how best to reduce water production. Companies have tried tubing patches, water shut off treatments and, most recently, Relative Permeability Modifiers (RPMs), which selectively inhibit water flow while having minimal effect on oil or gas production.Such remedial treatments, combined with top-side efforts like water injection, are being used in an effort to minimize the overall effect of produced water in Thailand. This paper presents, in a holistic approach, the issue of produced water in the GOT. Discussion of environmental issues, costs, disposal options and various methods that have been applied to deal with water production, are covered. Introduction Water production imposes an ever increasing burden on our industry.Improving technology, and the ability of oil companies to extract oil and gas from more marginal fields, will inevitably lead to increases in water as a percentage of total production.This has profound consequences for the economics of the fields involved.This increased amount of water production worldwide is also increasing the risk of environmental impact. Unwanted water production can result from coning, casing leaks, poor primary cement jobs (ie. channeling behind pipe), natural fractures, encroachment or injection water breakthrough and, no doubt, other plausible explanations exist.Over the years methods to reduce water production have been numerous, but there has been no single technology that can be considered either 100% successful or 100% applicable.Indeed, a cure-all technique for water production has best been described as the oil patch Holy Grail1.However, this has not deterred the ambitious engineer from pursuing the answer to this great challenge. In Thailand, three types of remedial jobs have been attempted to reduce water production - tubing patches, water shut off (WSO) jobs using crosslinked gels and RPM treatments.Each technique has limitations.In the case of mechanical tools (eg. patches), jobs can be complicated and can limit future re-entry by reducing tubing ID.For chemical WSO solutions, the zone of interest must be completely isolated from other zones and the mechanism that creates the blocking effect must not engage prior to the material being place exactly across the desired zone.The downside with WSOs has been the risk of hydrocarbon loss, as these blockers do not discriminate between good and bad fluids and they can sometimes "set" in the wrong place.Thus, polymers that do not require crosslinking and that could selectively reduce water production, without reducing hydrocarbon production, would be of great interest.Such is the case with RPMs.These polymers are water-soluble, hydrophilic and have the ability to attach to the formation matrix.In the presence of hydrocarbons they remain "de-hydrated" and have little affect on permeability.However, in the presence of water they "hydrate", producing long, rigid chains that decrease permeability.Because of RPMs selective reaction, they can be placed with simple "bullheading" techniques, which should make them, relatively, cheaper and less risky than other techniques.However, these materials have yet to prove their worth in the GOT due, perhaps, to the extremely high well temperatures prevalent there.