RIASSUNTO
SPE Members
Abstract
First introduced to the Gulf Coast region in 1987, the composite cutter bit is the result of research involving two design enhancements that combine polycrystalline (PDC) and thermally stable (TSP) cutters on one bit. Each polycrystalline (PDC) and thermally stable (TSP) cutters on one bit. Each cutter type provides complete bottom hole coverage alone, and, when combined in a 60% PDC/40% TSP mixture, greatly increases the range of applications for both.
The composite cutter bit is able to drill relatively hard, abrasive formations that contain large quantities of shale or shale stringers, achieving maximum penetration rates with extended bit life. Until now, neither traditional PDC nor TSP bits could successfully drill this relatively common Gulf Coast sequence of formation types unless the individual formations were relatively thick and their occurrence was predictable. Thus, composite cutter bits increase the already-proven predictable. Thus, composite cutter bits increase the already-proven benefits that PDC and TSP bits offer versus traditional rock bits or natural diamonds, and provide a viable drilling alternative to conventional bit selection.
Implementation of composite bits -- from the initial onshore Gulf Coast application into proven offshore applications - is described in several key case histories. Field data documents their introduction in the onshore Lac Blanc/North Freshwater Bayou fields, then details offshore successes in the Mississippi Sound, South Timbalier and Mustang Island areas. The case histories illustrate the broad range of well programs and drilling conditions in which these bits have performed. Successful application of composite bits now has spanned extreme variations in bit sizes, hydraulics, depths and lithologies.
Operating recommendations resulting from analysis of these case histories and mom than 100 composite bit runs are outlined. Analysis of this information has helped more clearly define the limitations and applications of composite bits in this region.
Introduction
The success of PDC bits in the Gulf Coast region is well known and documented. However, there are definite limitations to successful application of PDC bits in certain hard, abrasive formations located in this region. These limitations have led to development and successful implementation of TSP cutters.
While TSP cutters are successful in withstanding the higher temperatures generated by drilling sandstones, limestones and other abrasive formations, their performance has been limited by certain design configurations from drilling some of the relatively softer formations -- shales, in particular.
This paradox was addressed by development of two design enhancements: the first combined several 1/3 carat TSP cutters into a 1/2 inch cylindrical mosaic cutter. The second combined these 1/2 inch TSP cutters with traditional 1/2 inch PDC cutters onto one bit, known as a ""Mosaic"" or composite cutter bit.
Thus combined in a 60% PDC/40% TSP combination each cutter type would provide complete bottom hole coverage. The ratio was developed in provide complete bottom hole coverage. The ratio was developed in laboratory and field test programs, where it was determined to provide maximum rates of penetration, coupled with extended bit life.
SOUTHERN VERMILION PARISH The first composite bit applications considered are the Lac Blanc and North Freshwater Bayou fields located in Vermilion Parish in southern Louisiana. (Figure 1) These fields contain several abrasive sand-shale sequences at significant depths, and the sands may be pressure depleted.
Vermilion Parish experienced a dramatic increase in activity in 1985 as the result of five successful Miocene and several Oligocene field discovery wells. These wildcat successes followed high levels of leasing and seismic activity in the trend in 1994 that were due to then-recent Miocene discoveries. To date, more than 70 successful composite bit runs have occurred here, with the largest number taking place in the Lac Blanc field.
Lac Blanc Field
The first drilling project discussed occurred in the Lac Blanc field, which was discovered in 1957, and currently contains approximately 100 wells. These wells range in depths of up to 19,000 ft and are seeking gas and condensate production from a series of sands.
Geology
The region is located on the westward side of the Gulfward-plunging Mississippi Valley synclinal trough. The entire surface of the Parish is covered by Pleistocene and younger deposits which overlie extensive Tertiary and Mesozoic sediments.
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