fax 01-972-952-9435. AbstractA high performance water based mud (HPWBM) system has been used successfully to address a combination of drilling challenges faced in the Middle East. Drilling problems encountered in the area typically include shale instability through pressure transmission effects, swelling clay-stone, bit balling, drill-string accretion, differential sticking over tight gas permeable sands and down-hole losses. All these challenges can be very difficult to overcome with conventional water based mud (WBM) systems and can prove very expensive in terms of lost mud, lost down-hole tools, non performance rig time, side-tracks or ultimate failure to meet well or section objectives.The HPWBM system was introduced to provide considerable improvement in WBM performance and also provide an environmentally benign alternative to oil based muds (OBM) while emulating OBM drilling performance attributes. Recent applications in the Middle East have proved that the HPWBM system can be applied as an alternative to OBM, successfully achieving the objectives of the sections while providing drilling performance comparative to OBM. This paper discusses the technical features of the HPWBM system, gives an outline of previous applications and presents detailed case histories of the more diverse applications of the system and its components in wells in the Middle East, while comparing performance to offsets drilled with conventional WBM and OBM.
This paper describes the benefits and lessons learned from drilling 44 deep gas reservoir sections with sodium and potassium formate brine drilling fluids in Saudi Arabia's prolific Ghawar field from 2004 through 2008.Initially in Saudi Aramco, the formate brine drilling fluids were used primarily to prevent formation damage across the pre-Khuff sandstone reservoirs. As formate use burgeoned, their ancillary benefits such as stuck pipe mitigation, better bit performance, better than expected reservoir performance, lower pump pressures, torque and drag, solids content and enhanced temperature stability; use as a completion fluid and recyclability became evident.The fluids have been used in a variety of reservoir drill-in fluid applications in the pre-Khuff, Jauf and Unayzah sandstones with bottom hole temperatures (BHT) up to 323°F. The formates have also been used by Saudi Aramco in the Khuff carbonates for single and dual lateral horizontal wells where the drilling fluid overbalance to formation pressure sometimes exceeds 1,400 psi.In addition to the return permeability testing conducted prior to actually drilling the first wells with formates, the fluids nondamaging properties were proved up in the case of the Tinat-A well, a Unayzah-A re-entry/horizontal sidetrack, that had to be shut in for three years, due to a mechanical obstruction in the completion, with a 90 pounds per cubic foot (pcf) sodium/potassium formate completion fluid left in the hole as kill fluid. After removing the obstruction via a snubbing unit workover the well initially tested at 30 mmscfd with 4,320 psig FWHP, which was much higher than estimated.In a JFYN Unayzah B/C well, JFYN-A, only 1,214 ft of 5-7/8" hole was cut across the reservoir using a recycled 92 pcf potassium formate and the well flowed back at 45 mmscfd with 358 bopd oil on a 44/64" choke, which was also much higher than expected.Laboratory return permeability to gas test with Khuff-C cores showed 91% return permeability after flowing through the cores with potassium formate drilling fluid with 2% commercial lubricant as compared to 40% return permeability for the KCl Polymer drilling fluids of the same density normally used across the Khuff-C.The formates have also been used in combination with fine, medium and coarse calcium carbonate functioning as a bridging agent to drill in extreme overbalance situations across the Khuff-C reservoirs. The best example of this practice is UTMN-J, a Khuff-B re-entry sidetrack, where an 81 pcf sodium formate brine served as the base drilling fluid to drill and complete the 3675 ft horizontal section. The well was flowed back at a rate of 35 mmscfd without enzyme treatment or acid stimulation.
fax 01-972-952-9435. AbstractA high performance water based mud (HPWBM) system has been used successfully to address a combination of drilling challenges faced in the Middle East. Drilling problems encountered in the area typically include shale instability through pressure transmission effects, swelling clay-stone, bit balling, drill-string accretion, differential sticking over tight gas permeable sands and down-hole losses. All these challenges can be very difficult to overcome with conventional water based mud (WBM) systems and can prove very expensive in terms of lost mud, lost down-hole tools, non performance rig time, side-tracks or ultimate failure to meet well or section objectives.The HPWBM system was introduced to provide considerable improvement in WBM performance and also provide an environmentally benign alternative to oil based muds (OBM) while emulating OBM drilling performance attributes. Recent applications in the Middle East have proved that the HPWBM system can be applied as an alternative to OBM, successfully achieving the objectives of the sections while providing drilling performance comparative to OBM. This paper discusses the technical features of the HPWBM system, gives an outline of previous applications and presents detailed case histories of the more diverse applications of the system and its components in wells in the Middle East, while comparing performance to offsets drilled with conventional WBM and OBM.
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