fax 01-972-952-9435. AbstractDrilling the 16" hole section in Saudi Arabia's Deep Gas fields is particularly challenging due to a complex stratigraphic section that consists of carbonates interbedded with tough bands of hard stringers in addition to an abrasive sandstone followed by dense dolomite. The operator has attempted to efficiently drill the section using both roller cone tungsten carbide insert (TCI) and polycrystalline diamond compact (PDC) technology. The roller cone TCI bits had unacceptably low rates of penetration (ROP) with short bit life that required multiple runs to finish the required section. PDC technology delivered acceptable penetration rates but inconsistent run lengths due to impact damage from vibration induced by either the bit, bottom hole assembly (BHA) or formation change. The operator evaluated several PDC designs from different manufacturers but all suffered similar problems including short bit life due to impact damage.The operator determined to efficiently drill the section in one run and meet performance requirements would require new PDC/BHA technology. They organized a cross functional team to aggressively seek new PDC/BHA technology and state of the art motors and drilling practices to drill the interbedded rock section in one run. The team analyzed drilling operations from virtually every perspective using numerical models in addition to laboratory and field tests. The team identified PDC damage from BHA/bit whirl and vibration problems as the primary obstacle to achieving performance goals and focused their work on vibration management. The team performed BHA modeling analysis in order to develop a PDC solution that would minimize lateral and torsional vibrations. The modeling also helped determine the optimal range of operating parameters in order to meet performance requirements and eliminate BHA/bit whirl. The system solution combined high-power positive displacement motor to drive the bit harder and advances in PDC technology including improved bit stability and new cutter technology.Due to the collaborative effort, the operator completed the demanding 16" hole section for the first time in one run using the new BHA/PDC bit combination. The application of this new technology has reduced cost/foot from $195.84 to $121.59 for a total saving of $365,681 over 4,925 ft and 226 drilling hours. The average section ROP went up from 14 ft/hr to 21.8 ft/hr, a 55% increase in ROP resulting in 38% reduction in drilling cost.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractInterbedding of hard shale and sandstone sequences across the Lower Permian 'Unayzah and Jauf formations of Saudi Arabia which usually occur between 12,900 to 14,600 ft tvd, present unique drilling fluid density requirements such that 90-102 pcf (12.0-13.6 ppg) drilling fluids are often required to mechanically stabilize the shales while only 66-89 pcf (8.8-11.9 ppg) is needed to balance the 'Unayzah and Jauf reservoir pressures.One of the wells exhibited greatly improved drill string/wellbore lubricity, bit performance, reduced torque and drag, ECD's and pump pressures whilst inadequate drilling fluid density masked the full benefits of formate brine use on the other two. However, differential sticking did not occur in any of the wells.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe pre-Khuff Unayzah gas reservoir in Saudi Arabia is a competent sandstone formation with Unayzah-A and B/C sand units separated by a variable thickness siltstone unit, which is regarded as a sealing barrier between the Unayzah-A and Unayzah-B reservoirs. They are known to contain significant reserves of natural gas, however they are at low permeability, which has made it difficult to optimize production. Drilling through highly abrasive sandstone at high bottom-hole temperatures (BHT) has also been challenging. To meet Saudi Arabia's future gas requirements, it was essential to establish a means to exploit these reserves.Multiple methods have been used to drill and complete these wells, including long horizontals and multilaterals. Well trajectories were planned with the horizontal sections drilled along the direction of maximum in-situ stress (parallel to the fracture plane) for enhanced wellbore stability and fast penetration rates. Fracture treatments were pumped generating mostly longitudinal fractures propagating in the same direction as the maximum horizontal stress (parallel to the wellbore axis) resulting in a poor fracture network and suboptimal production results.In April 2010, a horizontal well was successfully drilled into the Unayzah reservoir towards the minimum in-situ stress direction and completed with an open hole, multistage (OHMS) fracturing system. A four-stage proppant fracturing job was successfully conducted in November 2010 without issues. Unique fracture signatures were observed in each zone and production from the well has exceeded expectations. This paper analyzes Saudi Aramco's successful initiative to drill the lateral section along the direction of minimum insitu stress and the challenges associated with wellbore stability, a highly abrasive formation and high static BHT. Also highlighted are Saudi Aramco's successful techniques for deploying the OHMS fracturing system with special emphases on borehole preparation. Lessons from the successful drilling/completion of this well could have a significant impact on how future Unayzah wells are drilled and completed to maximize productivity from tight gas reservoirs in Saudi Arabia.

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This paper discusses the planning and execution of the first successful short-radius sidetrack in deep gas drilling in Saudi Arabia. ANDR-XYZ was sidetracked from vertical at 12,242 ft and built inclination to 90° with maximum dog leg severity recorded as 39°/100 ft. Thereafter, a 2,400 ft lateral was drilled in the Khuff-B reservoir. Total depth was revised because of deteriorating reservoir quality. The operating time was 53 days versus 60 days planned. The short-radius sidetrack was one of three options (option 3, below):1. Sidetracking in the 9 5/8-in. casing set in the Khuff formation. Apart from cost reasons, this option was discarded because of high Jilh pressure requiring the mud weight to be increased from 102 pcf to 152 pcf, which would create well control and directional drilling difficulties.2. Milling the 7-in. liner, drilling a new 8 3/8-in. hole, setting a new 7-in. liner, and then drilling a 5 7/8-in. hole across the reservoir. Apart from being time consuming and costly, this option did not reduce technical complexity since it might have exposed the 9 5/8-in. casing across the liner lap. The condition of this section could not be guaranteed because of a previous milling operation while drilling the original wellbore.3. Re-entering the well by sidetracking in the 7-in. liner below the 9 5/8-in. casing. This required drilling a shortradius curve in the 5 7/8-in. section and continuing drilling and geosteering the well through the reservoir. Such a high buildup rate had never been successfully achieved before at this sidetrack depth in the Khuff reservoirs in Saudi Arabia.Several technical considerations were taken into account including the depth and type of whipstock, the length of rathole, design and analysis of the sidetrack bottomhole assembly (BHA) including torque and drag analysis, as well as overall operations strategy to achieve the well objectives. Several challenges were overcome and lessons were learned, which will be detailed in this paper.The successful delivery of this well resulted in saving of 45 rig days compared to the other options. The well also extended the frontier of drilling and workover options and opened up avenues to reenter several wells in deep gas drilling in Saudi Arabia.