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Cooper, C. (ChevronTexaco Energy Technology Co.) | Stear, J. (ChevronTexaco Energy Technology Co.) | Heideman, J. (ExxonMobil Upstream Research Co.) | Santala, M. (ExxonMobil Upstream Research Co.) | Forristall, G. (Forristall Ocean Engineering) | Driver, D. (BP America ) | Fourchy, P. (Murphy E&P Company)
Wisch, D. (ChevronTexaco Energy Technology Co.) | Stear, J. (ChevronTexaco Energy Technology Co.) | Versowsky, P. (ChevronTexaco North American Upstream, Inc.) | Welsch, J. (ChevronTexaco North American Upstream, Inc.) | Abadin, J. (ChevronTexaco North American Upstream, Inc.)
This paper will describe how the operator planned and drilled an eight-well sidetrack program, including one horizontal application, in Main Pass 299/144 field, Gulf of Mexico (GOM), in record time. This achievement was accomplished by improving operational efficiency (incident free) and reaching bottom hole objectives quickly, thus reducing open-hole exposure and costly "flat" time. The authors will discuss changes in the BHA, including mud motors, AKO settings, steerable ream while drilling tools and roller cone bits in addition to synthetic mud systems, that allowed each sidetrack operation to successfully drill oversize (eccentric technology) hole and hit the directional targets in record time.
The authors will discuss why different technologies were chosen and outline successful operations. A case study will be where a 7-5/8" steerable ream while drilling system with a 4-3/4" steel tooth pilot bit was able to build from 0° to 90° in one run, a record for the area.
Finally, the authors will document, with historical offset data, how improving operational efficiency and new bit technology reduced costs by approximately US$7.3 million on the eight-well program. Analysis will include a mechanical risk index that takes into account a variety of well variables to objectively compare costs on wells drilled in GOM.
The Main Pass 144/299 area is located approximately 100 miles southeast of New Orleans, Louisiana in the Gulf of Mexico in approximately 225 feet of water. Overburden consists of soft unconsolidated shales (gumbo) and Miocene reservoir sands. Production in the area is controlled by a large salt dome that acts to stratigraphically trap oil reserves. The first wells drilled in the area date back to 1962 with first commercial production established in 1967. The main focus in the field today is reentry projects to enhance production. The wells are drilled from jackup rigs cantilevered over the existing platforms. Most of the hydrocarbons in the area are produced through 2-3/8" or 2-7/8" tubing in 7" or 7-5/8" casing. The reentry wells are milled out of existing casing and vary from vertical to 20 degrees to horizontal. The producing sands are between 4000 ft to 10,000 ft TVD. The eight-well project utilized two jackup rigs drilling simultaneously, with each rig drilling four wells. The project (drilling & completion) was completed in approximately 67 days.
One of the most important aspects of improving drilling performance in the area was to document achievements as well as failures then objectively benchmark this data against the best in class. In mid 1999, the operator started to analyze offset drilling data in the GOM to compare its performance in Main Pass (MP) 299. Since complexity varies significantly from well to well, it was necessary to use an algorithm in an attempt to impartially compare one type operation against another. As a solution to this perplexing issue, engineers derived a Mechanical Risk Index (MRI). This mathematical computation takes into consideration, water depth (WD), measured depth (TD), kick off point (for sidetracks), true vertical depth (TVD) in addition to mud weight (MW) and horizontal displacement (HD) at TD. It also factors in the number of casing strings and several other drilling factors (DF) including "S" shaped well path, H2S or CO2 environment and the presence of hydrates or depleted sands with a differential greater than 3000 psi. Additional variable DF's include use of a subsea wellhead or mudline suspension system, if salt was penetrated or an open hole drilling size of less than 6-1/2" and/or if the well was horizontal. Although this method is not 100% accurate, it does help standardize well complexities for benchmarking purposes.