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Abstract Recent experiments and associated modelling on wellbore strengthening have revealed the importance of the filtercake in inhibiting the growth of fractures that would otherwise cause lost circulation. As a result, this increases the pressure that the wellbore can sustain, during both drilling and cementing. In preventive wellbore strengthening treatments, the rock formation is assumed to have no open fractures. Fractures are induced during the drilling process and the treatment inhibits their growth. This technique is most often used in drilling through depleted formations and has proven to be very effective. The basis of design is that particles of loss prevention material (LPM) in the drilling fluid are sized to enter the fractures, form a bridge within them, and then restrict fluid flow to the tip. A second mechanism has also been identified. Several hundred block tests on sandstone samples have been performed using various fluids, from drilling muds to cements, under various treatment conditions. These tests revealed the importance of filtercake in preventive wellbore strengthening. Particles sized to block a specific fracture were not needed. Provided that the filtercake itself can bridge the very narrow fractures that form at early times, it can prevent the fluid flow into the fracture that then allows the fracture to extend and widen. The properties, in particular the strength, of filtercake are important in determining the effectiveness of this kind of strengthening. Tests were performed to characterize filtercake and LPM effects on filtercake for both water and oil-base muds. Results showed that incorporation of particulate LPM to water-base mud filtercakes has little effect on the filtercake strength, but has appreciable effect on oil-base mud filtercake strength. Filtercake tensile strength is much more difficult to measure, particularly in relationship to the critical fracture width before the filtercake ruptures.
- North America > United States > Texas (0.28)
- Europe > Norway > Norwegian Sea (0.24)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.36)
INTRODUCTION ABSTRACT: We address the theoretical possibility of drilling with mud weights in excess of the least principal stress for cases of particularly severe wellbore instability. Tensile fractures initiate at the wellbore wall at Pfrac, they link up to form large axial fracturesub-parallel to the wellbore axis at Plink,?, and they propagate away from the wellbore at Pgrow. In general, our modeling shows that Pfrac and Plink,? can be maximized by drilling the wellbore in an optimally stable orientation, and Pgrow,? can be maximized by using "non-invading" drilling muds, that is, those that prevent fluid pressure from reaching the fracture tip (i.e., if solids in the mud form bridges within the fracture). In this paper we investigate theoretically the circumstances under which it may be possible to drill with mud weights in excess of the least principal stress in extreme drilling environments. To accomplish this we must avoid lost circulation due to the initiation and propagation of hydraulic fractures. We consider the case of an arbitraryoriented well with a perfect mud cake such that in the absence of hydraulic fracturing, no drilling fluids leave the wellbore. We consider a three fold strategy to increase, to the greatest degree possible, wellbore pressure during drilling. To accomplish this we utilize the facts that: (i) Wellbore pressure at fracture initiation varies with wellbore orientation, i.e., inclination and azimuth (Daneshy 1973, Hayashi et al. 1985, 1997, Peska & Zoback 1995). (ii) As deviated wells are generally not parallel to one of the principal stresses, multiple tensile fractures form at the wellbore wall in "en-echelon" pattern on opposite sides of the wellbore wall (Brudy & Zoback 1993). Wellbore pressure and wellbore orientation determine whether these multiple fractures link up or not (Weng 1993). (iii) When drilling with "high solids" water-based muds, pressures in the wellbore may not reach the fracture tip due to the narrow width of fracture and the bridging of solids within it (Black 1986, Fuh et al. 1992, Morita et al. 1996). Taking account of these facts, we show a theoretical model to estimate the critical pressures which dominate hydraulic fracture initiation and propagation. First, the pressure necessary to initiate fractures at the wellbore wall. Second, that required to link the inclined tensile fractures near the wellbore wall. Third, that required to extend the fracture unstably away from the wellbore. To the degree to which we can identify conditions which raise these pressures above the least principal stress, we can raise mud weights to deal with problems of extreme wellbore instability or in cases of extremely high pore pressure where the difference between the pore pressure and fracture gradient is quite small.
- North America > United States (0.68)
- Asia > Japan (0.68)
Making hole has become a more difficult and complex operation as operators move into untapped horizons, especially deepwater and unconventional fields. It is this increased difficulty that is driving a growing number of companies to invest millions of dollars in advanced materials that seek to make drilling wells easier. The technologies many are working on involve not mechanical systems, but advanced chemistry and physical science. Some are using nanoparticles and others are reworking older technologies by adding new substances, all in an effort to make the undrillable drillable. Those reaching for this prize include teams of university researchers, young technology startups, and established firms that are buying intellectual property from others so they can join the race.
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Pressure Management > Well control (1.00)
- Well Drilling > Drilling Operations (1.00)
- (5 more...)
Making hole has become a more difficult and complex operation as operators move into untapped horizons, especially deepwater and unconventional fields. It is this increased difficulty that is driving a growing number of companies to invest millions of dollars in advanced materials that seek to make drilling wells easier. The technologies many are working on involve not mechanical systems, but advanced chemistry and physical science. Some are using nanoparticles and others are reworking older technologies by adding new substances, all in an effort to make the undrillable drillable. Those reaching for this prize include teams of university researchers, young technology startups, and established firms that are buying intellectual property from others so they can join the race.
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Pressure Management > Well control (1.00)
- Well Drilling > Drilling Operations (1.00)
- (5 more...)
Drilling Fluid Technology Making hole has become a more difficult and complex operation as operators move into untapped horizons, especially deepwater and unconventional fields. It is this increased difficulty that is driving a growing number of companies to invest millions of dollars in advanced materials that seek to make drilling wells easier. The technologies many are working on involve not mechanical systems, but advanced chemistry and physical science. Some are using nanoparticles and others are reworking older technologies by adding new substances, all in an effort to make the undrillable drillable. Those reaching for this prize include teams of university researchers, young technology startups, and established firms that are buying intellectual property from others so they can join the race. Different groups are designing drilling-fluid additives and other materials that they claim make unstable wellbore walls stronger by preventing and sealing fractures as the drill bit eats its way down to the pay zone. The importance of these wellbore-strengthening objectives is well understood by drillers who have suffered sudden losses of drilling fluids into the rock formation through fractures, which can lead to gas kicks and catastrophic blowouts, or those who have had to deal with stuck pipe because of a collapsed borehole. For petroleum engineers, preventing these problems with new technology means they can design simpler, cheaper, and safer wells with fewer casing strings. For the boardroom, wellbore strengthening means executives can promise better returns and higher flow rates to investors because large-diameter casing strings can be placed into the production zone. And for the industry in general, wellbore strengthening means wells that many consider too dangerous or too hard to drill may soon become tamed. Clay-Stabilizing Nanoparticles for Water-Based Drilling Fluids In April, downhole chemical technology provider Flotek Industries acquired water-based, drilling fluid-additive technology from ARC Drilling Fluids. Flotek hopes to use the technology, which it markets as Microsolutions, in areas where using oil-based drilling fluids have traditionally been the only option. Drilling fluids that use water as a base are far cheaper than oil-based fluids, making them more desirable, but oil is less reactive with many rock formations. Wellbore Strengthening: The Mechanical Option Before many of the new chemical and nanoparticle technologies for wellbore strengthening arrived to the marketplace, casing while drilling (CWD) was used for more than a decade to mechanically achieve the same end. Weatherford International and other service companies have developed multiple technologies for CWD, as well as the similar method of liner drilling (LD). With CWD, the casing is the drillstring, and with LD, the liner is the drillstring.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.71)
- Geology > Mineral (0.70)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Pressure Management > Well control (1.00)
- Well Drilling > Drilling Operations (1.00)
- (3 more...)