Studies Dispel Myths, Give Guidance on Formulation of Drilling Fluids for Shale Stability

Abstract

CWwt 1S90, fADC/SPE Drilliw Confw-This pawr was prepe red fw Vesentation at the 1S9S tADC/SPE Drilliw CMferw held in Dallas, Texas, 3-6 Mti 1S9S. This paper ws selected for Wesenlatiw by an lADC/SPE Pregram Commitiee follewing review ef informalien contaln~h an abstrad submRted by the aufher(a). Centents of the peper, aa preaentad, have not baen reviewed by the Intamafimal Aaseciatiin of Drilling Centractora or the Society ef Petroleum Engineers and are subject to correefion by the a-s) w m~eriali aS WS~I~, d-~PSOEfllY M* any~a~~~he WC w SPE, tkir efficera, er members Paper8 preeanted qt the lAOC/SPE mear~s are suwect to publication raviaw by Edioriel Cmmittees cf the IADC and SPE. Elactronk reprcd~err, distriwm, w atore~ef any part ef this w fw eemm~ial mwa~~fhe Wffitan mnsenf ef the Seciety of Patrolw Eng*ra is @ibifed. Permission to mm h print is rastricfed to an abstract of net mere then W words: illuatratione may net be copied The abstract must eciWain -spiwous acknawtedgment & where and by whern the paper was presented. Wrte Librarian, SPE, PO. Box 83W3e, RWrdeon,~7~3-3e3S, U.SA., fax 01-972-9S2-9435. AbstractShale instability problems when using water-base drilling fluids have remained unresolved for decades because of a lack of knowledge and understanding of the shale hydration mechanisms. The industry has relied upon hydrocarbon-base drilling fluids for combating shale problems, but misconceptions have kept even those fluids from being utilized to their fullest advantage.With the use of hydrocarbon-base fluids now being curtailed because of environmental concerns, costs due to shale problems could escalate.The understanding of shale instability problems has been hindered by inadequate laboratory means of simulating contact of drilling fluid and shale under downhole conditions of stress and temperature. To address this situation Gas Research Institute has conducted a project in which laboratory equipment and procedures were developed to permit preserved specimens of downhole shale (cored in hydrocarbon-base mud) to be restored to in situ axial stress, horizontal stress, pore pressure and temperature prior to being drilled at a selected borehole pressure.Provisions were made for measurement of fluid transport in either direction between the circulating drilling fluid and the shale during an extended period of exposure. The borehole pressure was then reduced incrementally to observe for borehole failure and obtain a measure of effect of the &llling fluid on the relative stability of the shale.The above procedures have been used to study a wellknown troublesome Cretaceus shale cored using oil-base mud at a depth of about 5,500 ft in Block 4 of the U.K. sector of the North Sea.~is paper presents data showing that the aqueous activity of either a water-base or hydrocarbon-base emulsion drilling fluid can be adjusted to develop osmotic pressure that will cause water to enter or be extracted horn a low-permeability shale. The hydraulic differential between the borehole pressure and far-field shale pore pressure ...

Membrane Efficiency in Shale - An Empirical Evaluation of Drilling Fluid Chemistries and Implications for Fluid Design

“…16 That invert emulsion fluids and SBM can have significant membrane efficiencies has been demonstrated in experiments with invert emulsion fluids and shales which showed transport of water from a high-water activity shale to a low-water activity invert emulsion fluid, and the absence in the shale of exchangeable cations that were present in the invert emulsion internal phase. [17][18] On the other hand, measured osmotic pressures appear to be modest. Recently a maximum value of 1 MPa (150 psi) was reported for a shale, 19 which is consistent with the pressure differentials observed here.…”

Water-Based Muds and Shale Interactions

“…The most reliable tests are the ones that simulate high pressure and high temperature downhole conditions, with the top simulators that can afford drilling with real mud circulation and wellbore stability analysis 6 . The drawback is that they are very expensive and time consuming.…”

Avaliação do potencial uso de bioglicerina como base para formulação de fluidos de perfuração aquosos para poços de petróleo e gás

“…5,6 No entanto, apesar de apresentarem melhores performances que os fluidos aquosos, os fluidos oleosos apresentam custo elevado e elevada toxicidade. [7][8][9][10][11] Como uma alternativa às limitações de desempenho dos fluidos aquosos e para suprir às restrições ambientais impostas aos fluidos à base de óleo convencionais, surgiram os fluidos oleosos sintéticos de base orgânica, os quais utilizam como fase dispersante parafinas lineares, ésteres, éteres, alquilbenzenos lineares (LABs), olefinas internas (IO´s), olefinas alfa-lineares (LAO), poli-alfa olefinas (PAO), acetais e glicóis. 12 No entanto, mesmo esses fluidos sendo menos tóxicos e mais biodegradáveis que os de base oleosa convencional, é necessário considerar as restrições impostas pelos órgãos ambientais com relação ao descarte de fluidos e cascalhos gerados durante a perfuração no mar.…”

“…5,6 No entanto, apesar de apresentarem melhores performances que os fluidos aquosos, os fluidos oleosos apresentam custo elevado e elevada toxicidade. [7][8][9][10][11] …”