Dynamic Filtration During Microbit Drilling

Abstract

Drilling tests with a Ilk-in. diameter roller bit w.we perjormed on Berea and Bandera sandstones and Leuders Iime.$tone lising water (.tnd two conventional drilling muds us circulating f7uids to evaluate the influence of dynamic fi[trationon penetration rate. The muds possessed widely difierirrg API fluid-loss properties. Mud filtrate was constrained to f70w benea(h the bit: no filtrare fiowed radially (hrough the borehole wall. Rock pore pressure at three different loca/ic)ns ahead ojtltebit, cl~mu[ative fillrate volume, borehole pressure and bit location were monitored during drilling. The rock samples, cored in three orientations with respect to bedding planer, possessed a ;zide range oj[iqu!d permeabilitie.s, and were drilled at horeholet[)-f[)rtllatiotl pre,f.~liredifiererltial,v[)f 0,250, 500 and 1,000 psig. Theeflec! on penetration rate of API fh~idloss, borehole pressure and rock pertneability was studied. Rock pet-meability damage and pore pressure gradients beneath the bit were evaluated. The importance of boreho!e-tojormation pressure differential was i[lus(rated for each dri[ling J7w!dand rock permeability combination. Penetration rares decreased with increased boreho[e pressure and reduced fluid 10SS. The observed penetration rote reduction d{(e to changing fluid lo.rs was attributed to decreased fiitratef/ow and improved mud cake pia.stering by the low fluid-k).r, rmud. The reduction in filtrate flow cordd not i)e related to spurt-loss phenomena. Rock permeability influences penetration rate through particle invasion ahead of the bit, which datnage leads to high pt-essure gradients. Penetration rate variance with satnple orientation was evident for water -drilled sample,s but iess obvious for mud-drilled rocks. Pernteabi[ity damage beneath the b!t ranged from 1 to 3 cm. Maximum damage occurred in the first OS cm. Pressure gradients varied with API finid loss and could he correlated with penetration rate, The pressure gradient was found (O inffuence penetration rate in rock,vof al!permeabilities tested.

Dynamic Pore Pressure Ahead of the Bit

“…A large skin pressure drop is predicted for the rocks with high permeability because ofthe contrast in fluid diffusivity between the skin and the formation. 6. A significant pressure invasion is shown to take place at the depth of cut for the entire range of rock permeabilities (Fig.…”

“…10 3. Measurements of permeability as a function of depth ahead of the bit during microbit experiments 6 The skin transmissibility goes to T=4.59 md/m once the mudcake has been wiped out and to T= 121 md/m after the second operation. This clearly shows that all the permeability damage is very superficial, even in highly permeable rocks.…”

Applying Machine Learning to Predict the Rate of Penetration for Geothermal Drilling Located in the Utah FORGE Site

“…n numbers of regression trees are built on the n separated bootstrapped samples [20]. The n averaged predictions are explained by Equation (8).…”

“…An increase in MSE means that the system is foundering, and a disproportionate amount of energy is used for the given ROP. Young [8] demonstrated that ROP is influenced by the pressure gradient ahead of the bit. The latter cannot be measured in the field.…”

Clear Brine Drilling Fluids: A Study of Penetration Rates, Formation Damage, and Wellbore Stability in Full-Scale Drilling Tests

“…Microbit drilling experiments have provided valuable insight into the mechanisms affecting rate of penetration by eliminating field variables. [7][8][9] Whether such experiments simulate full-scale equipment under downhole conditions, however, is questionable.…”