User:DDSJman

1 Introduction 1.1 History and Applications of Directional Drilling Controlled directional drilling is the science of deviating a well bore along a planned course to a subsurface target whose location is a given lateral distance and direction from the vertical. At a specified vertical depth, this definition is the fundamental concept of controlled directional drilling even in a well bore which is held as close to vertical as possible as well as a deliberately planned deviation from the vertical. 1.1.1 Historical Background In earlier times, directional drilling was used primarily as a remedial operation, either to sidetrack around stuck tools, bring the well bore back to vertical, or in drilling relief wells to kill blowouts. Interests in controlled directional drilling began about 1929 after new and rather accurate means of measuring hole angle was introduced during the development of Seminole, Oklahoma field. The first application of oil well surveying occurred in the Seminole field of Oklahoma during the late 1920’s. A subsurface geologist found it extremely difficult to develop logical contour maps on the oil sands or other deep key beds. The acid bottle inclinometer was introduced into the area and disclosed the reason for the problem; almost all the holes were crooked, having as much as 50 degrees inclination at some check points. In the spring of 1929 a directional inclinometer with a magnetic needle was brought into the field. Holes that indicated an inclination of 45 degrees with the acid bottle were actually 10 or 11 degrees less in deviation. The reason was that the acid bottle reading chart had not been corrected for the meniscus distortion caused by capillary pull. Thus better and more accurate survey instruments were developed over the following years. The use of these inclination instruments and the results obtained showed that in most of the wells surveyed, drill stem measurements had very little relation to the true vertical depth reached, and that the majority of the wells were "crooked". Some of the wells were inclined as much as 38 degrees off vertical. Directional drilling was employed to straighten crooked holes. In the early 1930’s the first controlled directional well was drilled in Huntington Beach, California. The well was drilled from an onshore location into offshore oil sands using whipstocks, knuckle joints and spudding bits. An early version of the single shot instrument was used to orient the whipstock. Controlled directional drilling was initially used in California for unethical purposes, that is, to intentionally cross property lines. In the development of Huntington Beach Field, two mystery wells completed in 1930 were considerably deeper and yielded more oil than other producers in the field which by that time had to be pumped. The obvious conclusion was that these wells had been deviated and bottomed under the ocean. This was acknowledged in 1932, when drilling was done on town lots for the asserted purpose of extending the producing area of the field by tapping oil reserves beneath the ocean along the beach front. Many legal entanglements developed when it was established through directional surveys that oil was being removed from a productive zone under the tidelands, the ownership of which was claimed by both the town of Huntington Beach and the State of California. The state now supervises the Huntington Beach operations, and subsequently the art of cylinder drilling or drilling a prescribed “right of way" was developed . In 1933, during the development of the Signal Hill field in Long Beach, California, several wells were drilled under the Sunnyside Cemetery from locations across the streets surrounding the cemetery and even from more distant points to tap a productive zone underlying the cemetery. Controlled directional drilling had received rather unfavorable publicity until it was used in 1934 to kill a wild well near Conroe, Texas. The Madeley No.1 had been spudded a few weeks earlier and, for a while, everything had been going normally. But on a cold, wet, dreary day the well developed a high pressure leak in its casing, and before long, the escaping pressure created a monstrous crater that swallowed up the drilling rig. The crater, approximately 170 feet in diameter and of unknown depth, filled with oil mixed with sand in which oil boiled up constantly at the rate of 6000 barrels per day. As if that were not enough, the pressure began to channel through upper formations and started coming to the surface around neighboring wells, creating a very bad situation indeed. Many people felt that there was nothing to do except let the well blow and hope that it would eventually bridge itself over, and pray that it would do it soon so everyone could get back to work. In the meantime, however, a bright young engineer working for one of the major oil companies in Conroe suggested that an offset well be drilled and deviated so that it would bottom out near the borehole of the cratered well. Then mud under high pressure could be pumped down this offset well so that it would channel through the formation to the cratered well and thus control the blow out. The suggestion was approved and the project was completed successfully, to the gratification of all concerned. As a result, directional drilling became established as one way to overcome wild wells, and it subsequently gained favorable recognition from both companies and contractors. With typical oilfield ingenuity, drilling engineers and contractors began applying the principles of controlled directional drilling whenever such techniques appeared to be the best solution to a particular problem. Current expenditures for hydrocarbon production have dictated the necessity of controlled directional drilling, and today it is no longer the dreaded operation that it once was. Probably the most important aspect of controlled directional drilling is that it enables producers all over the world to develop subsurface deposits that could never be reached economically in any other manner. 1.1.2 Technology Advances The development of reliable mud motors was probably the single most important advance in directional drilling technology. Surveying technology also has advanced in great strides. The technologies complement each other. The development of the steering tool replaced the magnetic single shot instrument as a means of orienting a mud motor with a bent sub or housing. The tool was lowered by a wireline unit and seated in the muleshoe orienting sleeve. The wireline was passed through a circulating head mounted on a drill pipe and had to be retrieved every 90 feet. Data sent to the surface by the wireline was processed by a surface computer. Continuous updates were given on azimuth, inclination, temperature and tool face. With the advent of the side-entry sub, the wireline was passed through the side of the sub thus eliminating the need to pull the wireline every 90 feet. However, no rotary drilling was possible with the steering tool. In the early 1980’s ANADRILL MWD started to gain widespread acceptance as an accurate and cost-effective surveying tool. Today the MWD has virtually replaced the steering tool on kick-offs and is used exclusively with the steerable mud motor. A newgeneration MWD has been developed with the additions of gamma ray, resistivity, and DWOB/DTOR giving the MWD real time formation evaluation capabilities. Surveys obtained with the MWD are now widely accepted by both oil industry and regulatory agencies. Gyro technology has also progressed. The SRG (Surface Readout Gyro) is the latest addition to the survey line. It provides fast and accurate surveys electronically, eliminating the need to read a film base system. Many surveying companies provide their own tool: "FINDER", "SEEKER”, "GCT”, “FINDS", etc.