Influence of Pore Pressure on Drilling Response in Hard Shales

Gray-Stephens, Douglas; Cook, J.M.; Sheppard, M. C.

doi:10.2118/23414-pa

Cited by 17 publications

(8 citation statements)

References 11 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The number of factors hints at the complexity of the bit/rock interaction, something which is compounded by interdependence and nonlinearity in some of these effects. 6,7,11,15,18 Laboratory studies and modeling are however unraveling this complexity.…”

Section: Background To the Methodsmentioning

confidence: 99%

“…In permeable rocks for example, overbalance pressure influences ROP, 1 giving way to a dependence on bottomhole pressure as permeability decreases. [2][3][4] Overbalance pressure effects however are subject to dynamic influences, either via filtration effects on pore pressure in the bit/rock interaction zone, 5 or via stress effects on pore pressure around the wellbore. 6 Bit cleaning effects while drilling hydratable formations in water base drilling fluids ͑''muds''͒ may also override the effects of mechanical drilling parameters, so that rock mineralogy and mud chemistry are obviously significant factors.…”

Section: Background To the Methodsmentioning

confidence: 99%

“…Note that mud density effects are quantified by use of mud bottomhole pressure ͑''Mud BHP'' in the table͒, since this incorporates depth effects, and is probably the most influential pressure parameter in compacted shale drilling. 4 Pore pressure in the shales is, in any case, unknown to any degree of accuracy.…”

Section: Application Of the Methodsmentioning

confidence: 99%

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How to Improve Rate of Penetration in Field Operations

Fear

1999

SPE Drilling &Amp; Completion

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A method has been developed to identify which factors are controlling rate of penetration ͑ROP͒ in a particular group of bit runs. The method uses foot-based mud logging data, geological information, and drill bit characteristics, to produce numerical correlations between ROP and applied drilling parameters or other attributes of drilling conditions. These correlations are then used to generate recommendations for maximizing ROP in drilling operations. IntroductionTime spent drilling ahead is usually a significant portion of total well cost. In typical wells drilled by BP Exploration ͑BPX͒, this ''rotating time'' usually accounts for 10% to 30% of well cost. This means that the penetration rate achieved by the drill bit has considerable significance for drilling cost reduction.Despite this, the bit/rock interaction, and the ROP that results, is not well understood in detail. Other drilling phenomena, such as torque/drag modeling or directional behavior, are typically managed with the aid of validated, quantitative models. Such tools are conspicuously absent from planning or analysis of bit performance.Within drilling operations, uncertainty over expected ROP clouds decisions on which bit types and downhole tools to select to maximize ROP. That intuition is prominent in these decisions demonstrates the inability of drilling data or predictive models to provide anything more substantial.Against this background of commercial significance and technical difficulty, BPX is developing engineering methods to raise ROP. This paper describes one such method, and its application and benefits to one drilling operation.

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Section: Background To the Methodsmentioning

confidence: 99%

Section: Background To the Methodsmentioning

confidence: 99%

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How to Improve Rate of Penetration in Field Operations

Fear

1999

SPE Drilling &Amp; Completion

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“…Conversely, it is the absolute bottomhole pressure, independent of the far-field pore pressure that controls ROP in impermeable rocks (Gray-Stephens et al 1994).…”

Section: Impact Of Bit Design and Mud On Ropmentioning

confidence: 99%

Optimization of Deep-Drilling Performance—Benchmark Testing Drives ROP Improvements for Bits and Drilling Fluids

Judzis

Black

Curry

et al. 2009

SPE Drilling &Amp; Completion

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A critical cost in future deep-oil and -gas recovery is the cost to drill a well. This cost is dominated by the rate of penetration (ROP) that becomes increasingly important with increasing depth. Improving the technology of drilling and increasing the ROP was the object of full-scale laboratory testing conducted under a joint industry and Department of Energy (DOE) program titled "Improving Deep Drilling Performance" (Black and Judzis 2003). Simulations of deep-well drilling in the Arbuckle play and the Tuscaloosa trend were accomplished during 16 full-scale, high-pressure tests using four different 6-in. drill bits, three types of rock, and five different drilling fluids.This paper describes what is believed to be the first set of fullscale laboratory drilling tests yet performed at bottomhole pressures in excess of 10,000 psi. Accomplishments of the testing and analysis include the following:• Laboratory data was compared with field data to confirm that the simulated laboratory conditions provided similar results to what would be expected in the field.• ROP reductions were significant when "mudding up" at high bottomhole pressures.• Polycrystalline-diamond-compact (PDC) bits provided substantially higher ROP performance than impregnated or rollercone bits in the environment of this study.• The relationship between ROP and confined-rock strength is not a simple function of bottomhole pressure alone.• The mechanical specific energy (MSE) when drilling at high bottomhole pressure is often substantially higher than the rock's compressive strength, even when the bit is drilling efficiently.• Fluid invasion of intact rock and of rock broken up by the bit's cutting structure seems to play a major role in controlling ROP at these high bottomhole pressures.• Drilling-fluid compositions and properties that promote invasion without provoking formation damage, and bit-design features that facilitate the removal of rock debris from the hole bottom, hold promise for improving drilling efficiency in hard rock drilled at high bottomhole pressures.

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“…A number of the early laboratory studies showed that it was the difference between the borehole pressure and the pore pressure adjacent to the workfront which controlled pressure effects on penetration rate in permeable rocks (Eckel 1958;Eenink 1959, Van Lingen 1962;Black et al 1985). In contrast, it has since been shown that in impermeable rocks, or at least in hard shales, the absolute borehole pressure controls penetration rate independent of the initial pore pressure (Gray-Stephens et al 1994). The studies investigated basalt, dolomite, limestones, sandstones, shales, and even loose sand.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Borehole Pressure on the Drilling Process in Salt

Curry

Lourenco

Ledgerwood

et al. 2015

SPE/IADC Drilling Conference and Exhibition

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Wells penetrate long intervals of salt to access hydrocarbon reservoirs in many locations. High mud weights are frequently used to stabilise the wellbore while drilling through salt formations. High borehole pressures reduce penetration rates in many sedimentary rocks. This effect is significant and contributes greatly to the low penetration rates and high costs associated with deep drilling. This paper presents the results of an integrated laboratory study of the effect of borehole pressure on the drilling process in salt. The study included full-scale laboratory drilling tests, visual single-point cutter tests and triaxial compression tests. The drilling tests were performed using a Polycrystalline Diamond Compact (PDC) bit and a synthetic-based drilling fluid typical of field practice. The visual single-point cutter tests used a clear drilling fluid, enabling observation and video recording of the salt cutting process at elevated borehole pressures along with simultaneous measurement of the cutting forces.The effect of borehole pressure on drilling salt is seen to be small; increasing borehole pressure does not reduce penetration rates in salt as much as it does in many other sedimentary rocks. In contrast to other sedimentary rocks, salt deforms plastically to relatively large strains in compression without loss of mechanical integrity, even at low confining pressures. In addition, the shear stress to achieve a given strain does not increase greatly with confining pressure. Rock cutting forces in the single-cutter tests increased only moderately as borehole pressure was increased from 300 to 6,000 psi. Full-scale bit penetration rates also decreased by relatively small amounts over the borehole pressure range investigated (1,000 to 6,000 psi). Mechanical specific energy levels showed corresponding small increases. These levels, however, were consistently much higher than the compressive stresses required to cause even large strains at a confining pressure equivalent to the borehole pressure. Observations of the deformation and cutting processes in salt combined with results of finite-element analyses of rock and metal cutting explain the low sensitivity to borehole pressure of halite penetration rates and its relatively high specific energy.This study fills a gap in industry knowledge of pressure effects in drilling and sheds light on the processes involved in drilling rock salt. The key practical conclusions are that penetration rates and mechanical specific energy in salt are not greatly influenced by borehole pressure. Consequently, if a high borehole pressure is required to stabilise the wellbore through a salt formation, there is little penetration rate penalty to be paid, except perhaps if increasing the mud weight involves significant changes to the drilling fluid properties other than its density. The comparison of results from visual single point cutter and full-scale bit tests suggests, unsurprisingly, that reducing bit cutter density and modifying drilling fluid properties may both offer routes to ...

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Influence of Pore Pressure on Drilling Response in Hard Shales

Cited by 17 publications

References 11 publications

How to Improve Rate of Penetration in Field Operations

How to Improve Rate of Penetration in Field Operations

Optimization of Deep-Drilling Performance—Benchmark Testing Drives ROP Improvements for Bits and Drilling Fluids

The Effect of Borehole Pressure on the Drilling Process in Salt

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