Acid fracturing has been an integral part of Aramco's gas development strategy for the vertical wells in the Khuff carbonates over the last several years. The Khuff formation is a deep gas carbonate reservoir that is ideally suited for acid fracturing. During acid fracturing, the wormholes created by the reaction, results in excessive fluid loss. Controlling fluid loss is key to optimize acid fracturing treatments by creating longer and wider fractures. Diesel emulsified acid for deeper penetration and in-situ gelled acid, a polymer-based system, are used to control excessive leak-off at different stages of the treatment along with the alternating stages of polymer pad.These treatments in the vertical wells target several reservoir sub-layers with varying degrees of porosity and permeability contrast. These layers are often divided by anhydrite or dolomitic streaks that make vertical communication within the reservoir challenging. Hence acid fracturing ends up stimulating the highest reservoir quality zones with minimal contribution from the other zones in many cases.A pilot involving the use of a new degradable fiber technology designed to achieve effective acid diversion during acid fracturing was recently implemented. The pilot comprised field trials in a number of wells with similar reservoir characteristics and multiple porosity lobes. The fracturing treatments were designed and pumped with alternating stages of acid and fiber-laden polymer based pad fluid. The significant viscosity increase achieved in the pad by the addition of fibers and its particulate bridging mechanism would plug off the just stimulated zones effectively, thus diverting the new stage of acid into the non-stimulated porous zones. These fibers degrade and hydrolyze with temperature and time thus leaving the reservoir undamaged. This paper discusses the planning and design processes leading to the successful implementation of the technology, the experience during the stimulation treatment execution and the excellent post-stimulation results. Bottomhole pressure gauge data and production logs were run on these wells to ascertain the effectiveness of the technology and the results are discussed in the paper along with production history comparisons with offset conventionally acid fractured wells, and the lessons learned throughout the pilot.

Gas exploration wells are being drilled in high pressure and temperature environments targeting low permeability and high fracture gradient formations that push the envelope of conventionally used technologies. Thus, conventional perforating techniques are often not sufficient to break down the formation during fracturing operations in this type of wells.A novel system, specially designed to enable hydraulic fracturing in challenging producers was successfully field-tested. The system includes an anchor, a multi-cycle incrementing and stroking tool (MCIST), and a jetting sub with multiple nozzles. The anchor is used to prevent axial motion of the jetting head while jet cutting, which overcomes the long-standing problem of tubing stretch due to pressure changes and vibration during abrasive perforating operations. With the anchor as a depth reference base, the MCIST changes length upon command from the surface and uses sequential jetting to create a series of evenly spaced perforations in the casing, with corresponding large diameter longitudinal slots in the formation, in a controlled and evenly spaced fashion. The tool design and testing process, details about the field trial experience as part of a stimulation treatment, and the excellent post-stimulation results achieved are discussed in the paper.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAcid fracturing has been part of Saudi Aramco's gas development strategy to maximize productivity from for vertical wells in the Khuff carbonates over the last several years. During acid fracturing, the wormholes created by the reaction with the formation results in excessive fluid loss. Controlling fluid loss is one of the key objectives in acid fracturing treatments to be able to create longer and wider fractures, and hence maximize well productivity. Alternating stages of polymer pad with diesel emulsified acid for deeper penetration and in-situ gelled acid, a polymer-based system, have been extensively used in most fracture treatements in an attempt to control excessive leak-off during the treatment.

Saudi Aramco employed extensive matrix and acid fracturing treatments in thedevelopment of Saudi Arabian non-associated gas carbonate reservoirs.Thetarget reservoir is the Permian Khuff Formation which is the majornon-associated gas reservoir in the prominent Ghawar Field, eastern SaudiArabia.The Khuff reservoir is stratigraphically divided into fourcorrelative zones, namely Khuff-A, B, C, and D in downwardsequence.Khuff-B and C are the two major reservoirs with distinctivehydraulic characteristics. Khuff-A and D zones mostly are either discontinuousor have poor to non reservoir quality. Saudi Aramco is pursuing commingled production selectively as a part of thegas development plan to extend the well's economic life and to meet its growingdomestic gas needs. Since the Khuff-C has better reservoir quality with larger gas reserves, itwas completed by itself during the initial period of the fielddevelopment. Later, the commingled production by adding the Khuff-A and Bhas become part of the overall strategy to offset the natural decline fromKhuff-C and maximize gas production and extend the wells' life. This paper will review the acid fracturing and stimulation practicesemployed by Saudi Aramco in the Khuff-Carbonates. The criteria used to selectsuitable candidates for the commingled production and techniques employed toquantify flow contributions from each individual zone after commingling theproduction will be reviewed. The production performance, lessons learned, business impact and the way forward will be discussed. Introduction Since 1995, Saudi Aramco has embarked on an aggressive non-associated gasreserve development program and gas expansion projects.These projectsencompass the drilling of new wells and developing new reservoirs wherevercommercial gas reserves can be found. Developing the Permian Khuff-Carbonate reservoirs in the prominent GhawarField, eastern Saudi Arabia (Fig. 1) is in the center of this ambitious programto address the ever- increasing domestic energy requirement. Saudi Aramco employed extensively acid fracturing and high rate matrixacidizing stimulations to exploit the Khuff gas reserves. More than 200 Khuffgas wells hydraulic fracturing stimulations have been successfullyemployed. Saudi Aramco is pursuing commingled production selectively as a part of thegas development plan.Through case history examples, this paper will shedlight on the deployed stimulation practices, commingled production results, lessons learned, and business impact.

Acid fracturing has been an integral part of Aramco's gas development strategy for the vertical wells in the Khuff carbonates over the last several years. The Khuff formation is a deep gas carbonate reservoir that is ideally suited for acid fracturing. During acid fracturing, the wormholes created by the reaction, results in excessive fluid loss. Controlling fluid loss is key to optimize acid fracturing treatments by creating longer and wider fractures. Diesel emulsified acid for deeper penetration and in-situ gelled acid, a polymer-based system, are used to control excessive leak-off at different stages of the treatment along with the alternating stages of polymer pad. These treatments in the vertical wells target several reservoir sub-layers with varying degrees of porosity and permeability contrast. These layers are often divided by anhydrite or dolomitic streaks that make vertical communication within the reservoir challenging. Hence acid fracturing ends up stimulating the highest reservoir quality zones with minimal contribution from the other zones in many cases. Field trials involving the use of a new degradable fiber technology designed to achieve effective acid diversion during acid fracturing was recently implemented. The trials were conducted in a matrix acid and in an acid fracturing treatments, which were designed and pumped with alternating stages of acid and fiber-laden polymer based pad fluid. The significant viscosity increase achieved in the pad by the addition of fibers and its particulate bridging mechanism would plug off the just stimulated zones effectively, thus diverting the new stage of acid into the non-stimulated porous zones. These fibers degrade and hydrolyze with temperature and time thus leaving the reservoir undamaged. This paper discusses the planning and design processes leading to the successful implementation of the technology, the experience during the stimulation treatment execution and the excellent post-stimulation results. A production logs was run in the acid fractured well to ascertain the effectiveness of the technology. The results are discussed and compared in the paper with those from offset conventionally acid fractured wells, and the lessons learned throughout the pilot are also shared.