RIASSUNTO
Abstract
Since 1997 Saudi Aramco has attempted drilling its hard and ultra-abrasivePre-Khuff formations typically encountered from 13,000 to 17,000 ft TVD in andabout the Ghawar field of Saudi Arabia, with impregnated diamond bits run onhigh speed turbines, more commonly referred to as ""turbodrills"".
The turbodrill/impregnated diamond bit drilling assemblies were envisaged asa viable alternative to using impregnated, PDC, TSP and TCI bits on PDM's androtary drives. The PDC bits lacked the wear resistance required to drill thehard and abrasive sections of the Pre-Khuff economically due to limited bitlife and the TCI bits harbored a bleak history of excessive gauge wear and coneloss.
Three turbodrill/impregnated diamond bit runs were made in Pre-Khuffvertical wells from 1997 to 1998 all resulting in stuck pipe due to ""bitsticking"", where initially only the bit was stuck, as there was free rotationof the drillstring and turbodrill from the surface. Differential stickingand/or pack-off may have subsequently contributed to the pipe ultimately notbeing freed in each case.
After considerable review, redesign of the 8-3/8"" impregnated diamondbits, shortening of the turbodrill body and BHA with the use of a box-upconnection impregnated diamond bit, a respectable run of 242 ft averaging 10.3fph was made in HWYH-961, a vertical Pre-Khuff well across the 'Unayzah andJauf formations with cost of $443/ft.
With this success and enhanced understanding of the results of a recentconsultant firm's geomechanical analysis of the area that indicated the maximumhorizontal stress axis was East-West, Saudi Aramco felt they had a good chanceof successfully utilizing turbodrill/impregnated diamond bit drilling in thePre-Khuff without getting the bit stuck if the well was drilled parallel to thefield's maximum horizontal stress axis.
Finally, in 2003 the opportunity arose to test the wellbore stabilityhypothesis utilizing a turbodrill/impregnated diamond bit drilling assembly inwell WDHY-1, a 'Unayzah horizontal sidetrack. Two consecutive footage recordbreaking 5-7/8"" impregnated diamond bit runs of 737 and 852 ft were made on4-3/4"" steerable turbodrills in the horizontal section of the 'Unayzah-Bsiltstone and sandstone.
In 2004, four additional 4-3/4"" steerable turbodrill/impregnated diamondbit runs were made in the 'Unayzah-A and 'Unayzah-B formations with mixedresults. Three were made in HRDH-658 across an ultra hard streak at 89 in the'Unayzah-B, drilling with over 1500 psi overbalance to the formation with poorresults contrasted by a record breaking ROP run of 7.2 fph over 360 ft on thehorizontal sidetrack well TINT-3 across the 'Unayzah-A.
This paper chronicles the development and refinement of turbodrillingpractices and techniques across Pre-Khuff Strata in and around the Ghawar fieldof Saudi Arabia. It highlights the underlying rock mechanics principles, whichallow successful application of high speed turbodrilling with impregnateddiamond bits to horizontal wellbores but not in the vertical wellbores in thesame field, or more specifically in the case of TINT-3, a sidetrack of the samewell. Explanations are offered concerning the apparent enhanced bit, motor andturbodrill performance observed with the use of 90 pcf sodium/potassium formatebrine across the target reservoir.
Introduction
Saudi Arabia is best known as the world's largest oil producer averaging 8.1million barrels per day and for having the world's largest oil reserves (259.4billion barrels as of 2003 year end). The Kingdom also holds the world's fourthlargest natural gas reserves of 234.5 trillion standard cubic feet and produces6.9 billion standard cubic feet per day of non-associated gas1 .