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.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractActual worldwide oil production averages some 75 million barrels per day and, while estimates vary, this is associated with the production of 300 -400 million barrels of water per day. These values of approximately 5 -6 barrels of water for every barrel of oil are quite conservative. In some areas around the world, fields remain on production when the ratio is as high as 50 to 1.Water production causes several problems to oil wells such as scaling, fines migration or sandface failure, corrosion of tubular, and kills wells by hydrostatic loading, amongst other things. Thus, while water production is an inevitable consequence of oil production, it is usually desirable to defer its onset, or its rise, for as long as possible.Numerous strategies, both mechanical and chemical, have been employed over the years in attempts to achieve this. Simple shut-off techniques using cement, mechanical plugs and cross-linked gels have been widely used. Exotic materials such as DPR (disproportionate permeability reducers) and the new generation of relative permeability modifiers (RPM) have been applied in matrix treatments with varying degrees of success. Most recently, Conformance Fracturing operations have increased substantially in mature fields as the synergistic effect obtained by adding a RPM to a fracturing fluid have produced increased oil production with reduced water cut in one step, consequently eliminating the cost of additional water shut off treatment later on.This paper is an evaluation of various RPM materials commonly used on Conformance Fracturing treatments performed in the northeast of Brazil and other South American countries, rather than the usual laboratory testing methods and theoretical estimations. The paper also describes the technical design and operational methodology to treat single zone to laminated reservoirs with different mobility ratios. We believe conformance fracture techniques could significantly impact the development strategies of many fields worldwide.
Traditional "Best Practices" completion procedures recommend an acid pickle treatment to clean-out all tubulars in a wellbore prior to pumping an acid treatment or a "solids-free" completion brine system. The potential contaminants (iron oxidation, hydrocarbon deposits and pipe dope) can create formation damage if pumped into the formation during the main treatment. In addition, contamination of "solids-free" completion brine can lead to increased location diatomaceous earth (D.E.) filtration time. Tubing clean-out treatments normally consist of a slug of acid (10 to 15wt% hydrochloric) being pumped inside the tubulars and then reverse circulated back to surface without fluids being lost to the formation. A solvent is typically added to assist in the removal of pipe dope and organic deposits. Inhibitor and a surfactant, to facilitate wetting, are the normal fluid additives. Handling and disposal of this fluid after clean up of the tubulars can be dangerous and very costly due to its corrosive nature (pH <0). A slightly acidic (pH of 5.8–6.3) fluid has been evaluated in the laboratory for use as a pickling fluid to replace the traditional acids. This fluid's capability to remove iron scales on coiled tubing, prevent rust from reforming, clean up commercial pipe dopes and reduce corrosion rates, was compared to traditional hydrochloric acid. This fluid performed as efficiently as 15wt% hydrochloric acid in removing all potential contaminants associated with a workstring, while producing one fifth the corrosion rate. Furthermore, a work string treated with this fluid prior to being laid down on a pipe rack retained a protective coating that resisted re-oxidization for up to 30 days. Introduction Completion workstrings endure extremely harsh corrosive and erosive conditions during all phases of oilfield operations. As a result of these harsh environmental conditions, significant amounts of rust and iron oxidation are commonly present on the surfaces of the completion workstring, downhole pumps, and flowlines.1,2,3,5–8 Moreover, the surfaces of new low-carbon steel pipes and coiled tubing metals such as L-80 or N-80 are commonly covered with mill scale or oxidization after manufacturing and warehouse storage before even being subjected to well conditions. The dissolution of iron oxidation or mill scale solubilized in HCl acid during an acidizing treatment will form both ferric and ferrous ions in acid.9 Formation damage occurs when these iron compounds enter the perforations, sandpacks and /or the formation. Ferric ions precipitate as ferric solids once the pH value increases above 1–2.2,5–8 Another common completion contaminant in casing and tubulars is excess pipe dope. Pipe dope is used between drill pipe sections during preparation of the drill string to seal tubular joints and reduce thread wear. These materials are usually composed of very high viscosity grease with various fine particles, friction reducers and plating materials. The possibility of formation permeability damage is very high if the pipe dope is introduced into the producing zone. Pipe dope compounds as well as iron scales and rust may seal the formation, making acid treatment extremely difficult and inefficient. Introducing these contaminants into the formation can result in loss of well productivity if they enter the targeted oil-producing zone. Therefore, efforts to remove these contaminants before any chemical treatments begin are very advantageous to future well productivity. "Best practices" completion procedures recommend a pickle treatment to remove rust, iron oxidation and other possible contaminants from the completion workstring before certain treatments of completion stages are implemented. Pickle treatments are usually conducted before an acid matrix/acid fracturing procedure, gravel packing job or before introducing completion brine into the wellbore to prevent completion workstring contaminants from entering into the formation, perforations, or into the "solids-free" completion brine system.10 Introduction of contaminants into "solids-free" completion brines can also result in formation damage as well as increased rigsite D.E. (diatomaceous earth) filtration time. Also, contaminated completion brine can increase reclamation cost to the operator, when the brine is refurbished to new fluid specifications.
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