Wells drilled into the deep Bossier formations of the east Texas Hilltop Field encounter low-permeability, gas-bearing formations at over 15,000-psi pressure and 400°F temperatures. The wells require high-pressure fracture stimulations and extreme production drawdown to produce at economic rates. Wellbore temperature variations occurring between stimulation and production operations are extreme. The gases in these formations are also highly corrosive. Two of the first three wells completed in this area failed from casing collapse during completion operations or within the first few weeks of production. Finite element analysis (FEA) modeling coupled with log-derived formation properties confirmed that the extreme stresses applied to these wells rendered previous casings and cement sheaths "under-designed." Using an approach that combined formation, casing, and cement mechanical properties into a system, the wells were redesigned. Detailed thermal and mechanical modeling of all wellbore operations resulted in redesigned casings and a cement sheath more applicable to the extreme loads being exerted. Minor changes were also implemented to the job placement procedures to lessen the loads placed on the cement sheath. High-strength, corrosion-resistant casings and specialty cement designs were successfully used on the first two wells. Since those wells have been on production, additional wells have been drilled and completed using incrementally-simplified designs. All the wells have withstood multiple stimulations at treating pressures exceeding 14,000 psi, production test drawdowns at the perforations of over 13,000 psi, and temperature changes estimated at more than 300ºF. The wells have withstood these extreme pressure and temperature changes without failure of either the casing or cement sheath. The cement and casing designs employed have proven competent for the high-pressure, high-temperature (HPHT) conditions encountered. The successful design methodology couples well-specific casing and cement designs into a system capable of surviving the extreme pressure and temperature conditions imparted on the well during stimulation and production operations of deep, low-permeability HPHT gas sands. Introduction Construction of deep gas wells involves a large capital expenditure, and they are typically prolific wells. In addition, remedial work can be very costly, not only in terms of lost production, but also in the cost of materials and services needed to perform the work. Catastrophic well failure, although rare, does occur and can doom remaining reserves in place when it happens. Hence, there is a large incentive to do things right the first time. The traditional focus of the cementing job of designing adequate slurry properties and getting the slurry properly placed still applies, but that is only the beginning. As these wells are completed and produced, the cement sheath is designed to survive extreme stresses. Wellbore longevity will depend not only on how the cement sheath is designed to impart maximum sealing properties, but also on how it behaves when coupled to the casing and formation during all well operations. All operations and their associated timing with respect to the completeness of the cement hydration are "fair game" for investigation, including:Continued drilling operations (in the case of intermediate casings).Completion operations (e.g. completion fluid circulations and stimulation treatments).Well testing (e.g. pressure testing, severe drawdown tests, etc.).Access to various annuli for pressure control during thermal changes.The effects of gradual drawdown during long-term production.
This paper wee eelected for presentation by an SPE/lADC Program Committee following review of information oonteined in an abetract eubmiltad by the author(a). C-ontentaOf the paper, an pmented, have not bean reviewed by the International Aaaociatii of Drilling Contraotora or the Soc4aty of Patrolaum Enginaara and are subject to mrraotion by the author(a). The material, ee presented, done not neoaaaeriiy refleot any poetion of the SPE or IADC, their officers, or rnambem. Papers preaanted at SPHINX meetinge are aubjeot to publication review by Editorial CXrrnmiftaaa of the SPE and IADC. Permi.aabn to copy k reatriotad to an abatreot of not more than SW words Illuatrationa may not be copied, The ebatracf should contain oonspkwous eoknowledgment of where and by whom the paper in presented WrWe Llbrerian, SPE, P.O. Sox SSSSSS, Rkh.ardaon, TX 75W33SSS, U.S.A. Telex, 16S245 SPEUT.
A clarified xanthan drilling fluid was designed in order to replace the arctic diesel based drilling fluid conventionally used to drill horizontal wells in Prudhoe Bay. Use of this fluid in conjunction with well design changes has resulted in reduced drilling costs and increased well productivity.The fluid is designed to exhibit a true yield stress, which in conjunction with pipe rotation improves hole cleaning in high angle holes. The fluid is also non-damaging, provides shale inhibition, and is environmentally safe.
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