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.
If reservoirs engineers could drill wells, they would surely not drill a single, small diameter hole, with the walls of that hole damaged to the point they are initially impermeable! They would probably drill a hole with no damage to the walls, preferably with open fractures or wormholes emanating from that main hole. They would further likely construct more of a network of branches, mimicking the root structure of plants, evolved to efficiently drain nutrients from a soil reservoir. The problem, of course, has been that the technology required to create such a drainage system has been commercially unavailable. This situation changed, in Venezuela, in late 2005. This paper describes several wells where multiple, relatively short-length laterals were constructed, maintaining communication with the natural fracture network of the formation, imposing no damage. The paper details the target reservoir's properties and its history of poor production. The new production figures are contrasted to the historical field numbers. The method used was to simply dissolve a system of short laterals. This was achieved by pumping hydrochloric acid though a specially designed jetting assembly, attached to the bottom of a 1½″ coiled tubing unit. This revolutionary method not only creates a "reservoir engineer's" hole, it does so using simple equipment at a low-cost. Further details on the equipment are provided in the paper. The Dendritic Well - An Ideal Drainage System Natural processes often offer valuable insight into the most effective ways to exploit, or distribute, resources. Thus, the exchange of respiratory gases in the human body is accomplished by the provision of an enormous surface area for rapid gas diffusion, in the shape of the lungs. Similarly, oxygen, and other nutrients carried in the blood, are conveyed through a series of branching, progressively smaller conduits (arteries, arterioles, capillaries) to arrive at their target organs, and the process works in reverse (through capillaries, venules and veins) to transfer waste products for elimination. This type of network, for the collection or distribution of materials, is a frequently repeated feature in natural systems and clearly represents a highly efficient method to access resources, of one kind or another. Oil and gas wells are constructed with the intention of accessing and recovering hydrocarbons from permeable rock formations. Ideally, we would like to do that as quickly and as efficiently as possible. Unfortunately, however, we generally try to accomplish this goal by drilling only a few wells and depending on the native rock permeability, or the presence of natural fractures, to convey hydrocarbons to these few wells. This process is inefficient and, ultimately, leaves significant reserves unrecovered. It would be far more efficient, in terms of recovery and production capacity, if we could somehow construct wells that followed nature's tried-and-tested formula for optimising the process. Such wells would consist of a mother bore with a series of laterals, at different elevations, and each of these laterals would, in turn, subdivide into numerous smaller conduits. This approach maximises the contact between reservoirs and wellbore and distributes inflow across an enormous surface area. This is the "Dendritic Well" - until now, an impractical concept but one that may have some future with further refinement of the technique reported in this paper. Preferred Completion in Carbonate Formations Limestone formations are well suited for open-hole completion and this has become a preferred cost effective technique that also reduces deeper damage to the formation. However, it makes acid stimulation quite complicated, requiring special acid systems, and sophisticated mechanical tools, such as packers and or rotating jets, preferentially run with coil tubing, during the completion phase of the well. Stimulation uncertainties and effectiveness have caused some operators to elect completing wells with cemented casing so that selective acid stimulation treatments could be carried out where required.
fax 01-972-952-9435. AbstractFor over 50 years, mixtures of hydrochloric and hydrofluoric acids have been used for the removal of near-wellbore damage in sandstone formations. Such mixtures dissolve many siliceous minerals, including clays and quartz fines, the materials most frequently associated with particulate plugging of the formation pores. Unfortunately, the dissolution of these minerals is not a simple process and various chemical reactions can result in the generation of voluminous solid precipitates or colloidal gels. The appearance of such precipitates in the near-wellbore, can ultimately cause further formation damage and negate the benefit of the acid treatment.Other byproducts can be formed in sandstones containing carbonate minerals that react with acid and fluoride ions to produce the very insoluble calcium fluoride, CaF 2 , which is another potential source of formation damage. For this reason, traditional HCl:HF matrix treatments in sandstone formations are always preceded by a preflush, usually consisting of HCl to dissolve these carbonates. This approach is not always successful and adds to the complexity of the operation. The situation is worse in multistage treatments, which traditionally involve many repeat stages of preflush, main HF-stage, overflush and diverter. In such situations, it is difficult to ensure that the correct acid stage is always entering the appropriate zone and encountering the appropriate mineralogy. The result can be poor zonal coverage, poor damage removal, creation of unexpected damage due to acid/rock incompatibilities and, ultimately, poor stimulation results. This paper presents the results of a new acidising technique that eliminates the need for preflushes, across a wide range of mineralogies. It describes the background to this approach and reviews the results of laboratory testing and field treatments. It concludes with a matrix acidising methodology that can improve logistics, reduce cost and improve results while, simultaneously, making treatments easier to implement and control, at the field level.
Malaysia is a significant gas producer and LNG exporter within Asia-Pacific region. Many of the country's gas fields are offshore carbonate reservoirs. The exploitation of these reserves involves drilling horizontal wells for maximizing reservoir contact and hydrocarbon drainage. Many of these wells experience drilling mud damage. One of the challenges in stimulating long horizontal wells with open-hole completion is the placement of stimulation fluids for effective zonal coverage and generating wormholes to pass the damaged zone. Placing gelled acid through coiled tubing has been the standard practice to clean up the wellbore. Due to the low pumping rate, stimulation results have been limited. A change was initiated aiming to have the acid pass the damaged zone and generate wormholes through effective diversions. This paper describes the application of acid/diversion systems and pumping schedules to improve acid coverage. The selection of in-situ crosslinked and particulate diverters through laboratory testing is described as well as the implementation of a unique mixing system. Several case histories are presented illustrating the effectiveness of the fluid systems and mixing process in improving well productivity and job economics. A stimulation campaign was executed in 2006 to utilize the systems selected in long open-hole horizontal carbonate gas wells. To maximize the results, the following have been practiced:Clean up and test the wells after completion to get initial productivity.Bullheading acid to increase pumping rate.Use a mixing-on-the-fly unit in limited barge space.Learn from previous jobs to improve subsequent ones by optimising pumping procedures.Clean up and flow test right after stimulation to evaluate results. 7 wells were stimulated in the campaign. Significant gain has been achieved through progressively optimising pumping procedures. Indication of diversion was observed compared to previous practices. Stimulation cost is less than that of using coiled tubing. Background In Malaysia under the Production Sharing Contract (PSC) with Petronas, Sarawak Shell Berhad together with its equity partners are under contract to develop and produce natural gas resources. Under the PSC framework gas produced will be supplied under a gas sales contract to the MLNG plants as shown in Figure 1. Long horizontal wells are drilled where there are no compartmentalization or baffles in the carbonate reservoirs. In addition the wells are completed with large tubing size (7.5/8" tubing). The wells are cleaned up using a clean up package; stimulated with acid; further cleaned up before being tied into the production facilities. Tradiitionally coiled tubing has been used for the placement of acid. Acid treatment volume used is typically 10 gal/ft, which is relatively low. The gelled hydrochloric acid (HCl) is mixed in batch tanks. Typically the average horizontal length is 2000 ft and the mixing of 20000 gal can take up to 24 hours due to the confined space on the drilling barges and the number of acid carboys available. Handling and mixing large volume of acid can be a logistical nightmare especially when there are more than 2 horizontal wells that require stimulation per campaign.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAlthough hydraulic fracturing is a routine stimulation technique in many parts of the world, it has seen limited use in areas such as Asia Pacific for example. Among the hurdles to fracturing in traditional non-frac markets is the common perception that fracs are expensive, risky, complex and difficult to design. This perception has been challenged in recent years by the promotion and technical validation of simplified fracturing treatments aimed, primarily, to address near-wellbore skin damage. The new approach, termed Skin Bypass Frac (SPF), is low cost, safe, simple, and easy to design. In fact, by careful fluid selection, these small treatments can be pumped from an offshore drilling rig using nothing more than cementing equipment. By simplifying fracturing to this degree, there is now a safer and more environmentally-friendly way to remediate skin damaged wells, without the implicit dangers of acidising.To date, this technique has been used in a number of diverse situations yet, despite its simplicity, it has yet to be practised on a widespread basis. Results indicate that if candidate selection is good, production increments can be significant, particularly in those wells with skin damage. To make candidate selection effortless, a set of criteria was developed to determine which wells would benefit the most. Parameters such as permeability, zone height, estimated skin, reservoir mobility, zone isolation and proximity to water were all considered in this selection model. This paper reviews the practical theory of using small simple frac treatments to improve productivity in damaged wells and wells with small sands where higher recovery rates are desired. The concept of LCP is discussed and a model is put forward to perform frac jobs with cement units, which may come to be known as universal pressure pumping units.
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