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Abstract

Recent technological advances are driving casing and liner drilling from a niche market into the mainstream environment. Improved connections, tubulars, advances in rig technology and pipe handling have enabled operators to consider drilling with casing/liner as an option on many new wells[1,2].  Escalating deepwater costs and the need to further reduce onshore drilling expenses in low cost fields continue to push the technology forward. 

In a mature South Texas field, an operator discovered the difficulties of drilling into formations with weak matrix strengths, loss circulation zones, and tight pore pressure/fracture gradient windows. These issues have deemed the field sensitive to aggressive drilling techniques and the operator has been forced into a conservative drilling program with reduced flow rates and lower weight-on-bit capacity. The operator needed to reduce trouble time, lower costs and make the wells more economically feasible. 

A service company introduced a new liner drilling system solution to get through the extensive problematic zones. The system is engineered so the operator can ream to bottom and then continue drilling with the liner to the required target depth. The system is comprised of a drillable fixed cutter casing bit and a drill-in liner assembly designed to handle the rigors of a drilling environment (rotation, reciprocation and drilling torque). The liner system utilizes a running tool that allows the liner to be used in drilling mode handling all the required drilling loads without fear of release. Once at desired setting depth, the hydraulically balanced liner-running tool is released with a setting ball. The casing bit is manufactured from a specialized steel alloy that allows technicians to braze polycrystalline diamond compact (PDC) cutters directly to the one-piece bit ensuring a robust cutting structure capable of efficiently drilling new formation as well as reaming existing hole. The system allowed the operator to drill in the liner to TD, cement, and then drill out to the next casing point.

To date, nine intervals have been drilled with this system in South Texas. This paper will focus on the problems encountered in the field, the development work in establishing a solution for the operator, the results attained, and lessons learned through using this new technology.

Introduction

Gas fields in South Texas have been developed and operated for the past 50 years.  These high pressure, high temperature (HPHT) wells are drilled to an average depth of 14,000 ft. The bottom hole temperatures range from 280-400ºF. Most wells have multiple low permeability pay sands, which require massive hydraulic fracture treatments to produce economically. Each pay interval is fracture treated in a separate stage and the production from all the sands is commingled. Most of the wells are completed as “tubingless” or cemented completions, utilizing 3-1/2” or 2-7/8” production tubing. 

Current drilling activity is in and around mature fields where large volumes of gas have been produced. Severe reservoir pressure depletion intermingled with high pressure is often encountered. The presence and level of pressure depletion is difficult to predict due to complex geology, low permeability and production from several sand members that have been commingled. Pressure depletion in the productive pay interval has caused the overlying formation to become unstable, which has resulted in reduction of the fracture gradients immediately above these depleted sands. This fracture gradient reduction has resulted in very tight pore pressure/fracture gradient margins approximately 2,000 ft above the main productive zones and through the depleted sand intervals.