RIASSUNTO
SPE Members
Abstract
This paper describes the design and application of new bi-center bit technology in the Bay Marchand Field (offshore Louisiana). A bi-center bit and tandem motor assembly were used to simultaneously drill, underream, and directionally control a slim hole horizontal re-entry well using conventional directional techniques. This new bi-center technology significantly reduced cost for underreaming and eliminated the risk associated with the use of underreamers in a slim hole, high angle environment.
Introduction
The increased horizontal drilling activity in the Gulf of Mexico over the last several years was a precursor to the proliferation of horizontal sidetracks from existing wellbores Perhaps nowhere is the possibility for the successful application of new slim hole re-entry horizontal drilling techniques more evident than in the Gulf of Mexico. Since the drilling of the first horizontal re-entry well in this area in early 1994, slim hole horizontal re-entries have stressed the new technology envelope in all aspects of drilling operations as operators strive for new cost-effective methods to enhance profitability and justify additional projects. Slim hole applications as found herein will give direction to improved field management through the utilization of existing wellbores.
One aspect of drilling horizontal re-entry wells which presented an opportunity for the infusion of new technology was found in the elimination of the high costs and risks associated with using underreamers in a slim hole high angle environment. The problem lies in drilling a slim hole horizontal re-entry well out of an existing 7"" casing string. Typical horizontal well drilling and completion designs require the well be horizontal just before or as the objective sand is drilled. Casing is then run to isolate this hole section and protect the future lateral ""productive"" section of the hole from mud contamination or borehole sloughing. When drilling this intermediate hole section from a 7"" cased wellbore, typical hole sizes range from 5-7/8"" to 6-1/8"", depending on the weight of the 7"" casing. A hole size of 6-1/8"" allows proper clearance for no larger than a 5"" casing string. With 5"" casing in place, additional risks are encountered while drilling the lateral section since the available tools and equipment required are 3-1/2"" in outside diameter. Conventional external fishing techniques cannot be employed to fish tools of this size through 5"" casing.
The use of current technology necessitates the underreaming of the intermediate hole section in order to accommodate the 5-1/2"" casing string. Conventional slim hole underreamers have been used to resolve the problem, but not without mechanical concerns and excessive costs. Although conventional underreaming is fairly reliable, special caution needs to be employed when using these tools in a slim hole application where the underreaming blades have limited life and shock resistance and lend themselves to more frequent failures. This can lead to costly fishing operations.
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