SPE煤层气英文翻译.doc
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1、毕业设计(论文)外文翻译学生姓名:田晓学 号:xxx 专业班级:石油工程指导教师:王明教授 2012年6月10日原文: tate of the Art in Coalbed Methane Drilling Fluids现代煤层气钻井液工艺水平Len V. Baltoiu ,Brent K. Warren, QMax Solutions Inc,Thanos A. Natras,Encana CorpAbstractThe production of methane from wet coalbeds is often associated with the production of sig
2、nificant amounts of water. While producing water is necessary in order to desorb the methane from the coal itself, the damage from the drilling fluids used is difficult to assess because the gas production follows weeks to months after the well is drilled. Commonly asked questions include: What are
3、the important parameters for drilling an organic reservoir rock that is both the source and the trap for the methane? Has the drilling fluid affected the gas production? Are the cleats plugged? Does the “filtercake” have an impact on the flow of water and gas? Are stimulation techniques compatible w
4、ith the drilling fluids used?This paper describes the development of a unique drilling fluid to drill coalbed methane wells, with a special emphasis on horizontal applications. The fluid design incorporates products to match the delicate surface chemistry on the coal, a matting system to provide bot
5、h borehole stability and minimize fluid losses to the cleats, and a BREAKER method of removing the matting system once drilling is completed.Field results from three horizontal wells will be discussed, two of which were drilled with the new drilling fluid system. The wells have demonstrated exceptio
6、nal stability in coal for lengths to 1000 m, controlled drilling rates and ease of running slotted liners. Methods for, and results of, placing the BREAKER in the horizontal wells are covered in depth.IntroductionProduction of methane from coal has become one of the more interesting practices in rec
7、ent years to produce hydrocarbons.1-6 In the United States in 2005, it is estimated that 11.7% of all gas produced is from coalbed methane (CBM) sources7.While in conventional drilling in sandstones and carbonates it is often simple to tell if a drilling fluid is fully or partially responsible for f
8、ormation impairment, this is often much more difficult in CBM wells. When a CBM well depends upon the production of water to reduce formation pressure and thus lead to gas desorption, the influence of drilling fluid becomes masked or even forgotten.As the frontiers of CBM wells are pushed into the h
9、orizontal drilling realm, the importance of the drilling fluid is magnified. The fluid needs to both stabilize the wellbore during the drilling phase, but at the same time needs to minimize any production shortfalls due to damage. A simple N2 fracture which may be used on a 5-10 meter vertical coal
10、seam is not a simple matter to transfer to a 500-1000 meter horizontally drilled coal section.This paper discusses how coal geology impacts drilling planning, drilling practices, the choice of drilling fluid and completion/stimulation techniques for Upper Cretaceous Mannville type coals drilled with
11、in the Western Canadian Sedimentary Basin. A focus on horizontal CBM wells is presented.Basic Coal GeologyIf you were to hand a piece of coal to someone you knew and asked them to describe it, they would probably say “its black”. The fact is they are right, but there is more to coal than what meets
12、the eye, especially if you dont know what youre looking for. Coal is a very complicated organic rock made up of tiny microscopic constituents called macerals, which are analogous to the minerals found in inorganic rocks such as quartz. Macerals are made up of various lithified plant debris such as s
13、pores, resins, pollens, waxes, cuticles, and resins. There are three main groups in which macerals are classified, the vitrinite group, inertinite group, and the liptinite group, all which can be broken down further in to several individual macerals. Macerals of similar character can be grouped into
14、 what are called microlithotypes, microscopically discernible units analogous to laminations in sedimentary rocks such as sandstones. Microlithotypes are further combined to form macroscopically visible units called lithotypes. Lithotypes, which are analogous to beds in other sedimentary rocks, are
15、classified on the basis of their brightness. For example, a lithotype predominantly made up of the vitrinite group would look very bright. In contrast, coal rich in inertinite would look very dull. The dull and bright bands tell us something about the heterogeneity of the coal and how variable its p
16、hysical make up is both vertically and laterally. Each lithotype comes with its own set of physical properties which can enhance or impede production of coalbed methane.Coal rank is another important physical property. Coal rank is a measure of the degree of chemical alteration the coal has undergon
17、e (also referred to as diagenesis). The longer the coalification process goes on, the higher rank the coal becomes. Vitrinite content also changes with coal rank, as do several other physical properties important to CBM potential8 (Figure 1).Figure 1 Coal Ranking Classification by Vitrinite Reflecta
18、nce, Volatile Matter, Bed Moisture and Caloric ValueCleatingThe single most important physical characteristic of any coal relative to CBM production is permeability. Permeability in coal is a direct function of the cleat and/or fracture network present. As coal matures through the process of coalifi
19、cation, moisture and volatile gasses are slowly driven off resulting in the shrinking of the coal matrix. As the coal shrinks, cleats begin to form, similar to the cracks that develop when mud dries under the heat of the sun. The cleat/fracture system in coal is also referred to as the macropore sys
20、tem.A good metaphor for visualization is a loaf of sliced bread (Figure 2). The spaces between the slices of coal are fractures that are referred to as “face cleats”. The spaces within the slices of coal are referred to as “butt cleats”. They may, or may not, intersect with the face cleats. When we
21、refer to coal “permeability” we actually refer to the permeability obtained from the fractures network. Face cleats are very important as they are the backbone of coal permeability. Butt cleats may, contribute to such permeability if they intersect the face cleat network. A third set of fractures ma
22、y be found on coals that have been exposed to tectonic stresses. These third sets of fractures are referred to as “tectonic fractures” and are very important to CBM production. Tectonic fractures increase the permeability of the coal by two mechanisms: (a) their own presence and (b) by connecting to
23、 some of the butt cleats previously not part of the fracture network. With the great heterogeneity within a single coal network, the range of fractures presence can vary from no fractures to complete three-set fracture development.Figure 2 Stylized depiction of a coal showing the face cleats , butt
24、cleats and tectonic fractures Maceral type and coal rank are the two most important controlling factors in cleat development. For example, a vitrinite rich high ranking coal will have excellent potential for cleat development. In contrast an inertinite rich, low rank coal will have very little poten
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