This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 140332, ’Understanding and Managing Bottomhole Circulating Temperature Behavior in Horizontal High-Temperature Wells - A Case Study Based on Haynesville Horizontal Wells,’ by Keith Trichel, SPE, and John Fabian, SPE, Baker Hughes, prepared for the 2011 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 1-3 March. The paper has not been peer reviewed.
While high-temperature (HT) wells have always presented drilling challenges, the recent activity increase in the Haynesville shale along the border of Texas and Louisiana presents an extreme environment for drilling equipment. Along with a high frequency of temperature-related measurement-while-drilling (MWD) and logging-while-drilling (LWD) failures, the profile and architecture of Haynesville wells have provided an opportunity to study and understand the thermal behavior of horizontal HT wells in general. Thereby, well-specific operational guidelines and planning considerations can be implemented to reduce the risk of downhole temperature-related failures.
The Haynesville covers approximately 9,000 sq miles. The Haynesville basin could contain up to 250 Tcf of technically recoverable gas, making it one of the largest gas plays in the USA. Production is from the Bossier and Haynesville shale formations, which correspond in many areas, so the names often are used interchangeably. The Haynesville has average thickness of 200 to 300 ft, and the depth ranges from 10,500 ft in the northwestern part of the basin to 13,500 ft in the southeastern extremities. This play is one of the deepest shale plays, and, therefore, downhole conditions are more difficult. Bottomhole temperatures (BHTs) have been measured on the order of 380°F.
A typical Haynesville well requires 35 to 45 days to drill. The intermediate section may be drilled with either water-based mud (WBM) or oil-based mud (OBM), at the operator’s discretion. Soft sediments are encountered in the upper section below surface casing, but very hard and abrasive zones are found in the lower portion when passing through the Travis Peak and Cotton Valley formations. Completing the intermediate-hole section in a single polycrystalline-diamond-compact-bit run is difficult. Most horizontal sections in the Haynesville are drilled with OBM and experience high bottomhole circulating temperatures in the range of 300 to 350°F, mud weights of 15 to 17 lbm/gal, and high stand-pipe pressures of approximately 4,000 psi.
The combination of OBM, high temperature, and high solids content in the mud is a challenging environment for downhole motors, but motor failure is not the leading cause of unplanned trips. Often, the high bottomhole circulating temperatures exceed the normal temperature rating of MWD/LWD electronics, typically 302°F. To address this need, some directional-service companies offer specially screened tools rated to 320°F while others offer high-temperature tools rated to 350°F. Even with this technology, recent trends indicate that the leading cause of unplanned trips in the Haynesville is likely to be failure of the MWD/LWD electronics.