A Novel Technique to Acidize Horizontal Wells with Extended Reach

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling horizontal wells with extended reach is intended to maximize reservoir drainage and minimize water production due to water coning. However, an inherent problem with these wells is poor acid distribution during matrix acidizing, especially in reservoirs with high permeability streaks. This paper discusses an innovative approach to treat horizontal wells with extended reach. This new technique comprises mechanical diversion in the wellbore, and chemical diversion in carbonate formations.Coiled tubing has been used for years to better distribute the acid in vertical and horizontal wells. However, application of coiled tubing in long horizontal wells is a function of wellbore diameter and length. Coiled tubing cannot reach the total depth of the well if there is large washout, or if the length of the openhole is greater than what the CT can reach. The maximum length that CT can reach depends on the length of the reel, diameter of the coil and wellbore geometry. To extend this length, we have used a hydraulic tractor to pull the coiled tubing to the total depth of the well. This will ensure better acid distribution over the wellbore. To enhance acid diversion in the formation, a visco-elastic surfactant-based acid system was employed.Wells selected are horizontal that were drilled in a carbonate reservoir in the oil fields (both land and offshore) that are present in the eastern part of Saudi Arabia. The total length of the target zone for the well "A" and well "B" is 13,543 and 20,304 ft, respectively. Typical coiled tubing (1 ¾-inch) cannot reach the total depth in these wells (CT lockup length is 10,300 ft for well "A" and 13,200 ft for well "B").A special hydraulic tractor was used to pull the coiled tubing to the total depth of these two wells. A visco-elastic surfactant based-acid system was utilized to remove formation damage induced by the drilling fluid (water-based mud) and enhance the permeability of the formation in the critical wellbore area. Corrosion inhibitor and other acid additives were carefully selected to maintain the integrity of well tubulars, coiled tubing and the tractor (metallic parts, O-rings and seals of the tractor). Before attempting the stimulation of the extended reach well, a water jetting method was adopted to remove near well bore damage resulting from the drilling mud cake and mud invasion. Production logging tests were conducted after drilling the well, after the water jetting treatment, and after the matrix stimulation. The productivity index of the well decreased after the water jetting treatment. However, the acid matrix treatment delivered through the CTtractor nearly doubled the productivity index of the treated well.

A Novel Technique to Acidize Multilateral Open Hole ER Horizontal Wells Drilled in Carbonate Formations

“…The surfactant used was amphoteric and the rheological properties and field cases using this system were given in previous publications. [24][25][26][27][28] Tables 3 and 4 give the acid formulations used. The acid volume used in both wells was 10 gals/ft of open hole.…”

“…Openhole sections of up to 2,000 ft were successfully stimulated by bullheading the treating acids at the CT lock-up depth. 26,27 A major advantage of viscoelastic surfactant-based acids over conventional gelled acids is that they do not contain polymers and hence they are less damaging. Unlike other diverting materials, such as foam and particulates, viscoelastic surfactant-based acids can be pumped as a single fluid, which will stimulate and divert at the same time.…”

“…This fluid proved to be very successful in bullheading operations for long perforated intervals 24 and short OH horizontal sections. 26,27 The in-situ stimulation and self-diverting properties of the viscoelastic surfactant-based acid system made it the fluid of choice in this application. The diversion capability of the fluid tends to extend the reach of acid coverage to other non-stimulated sections.…”

Evaluation of Acid Treatment Results for Water-Injector Wells in Saudi Arabia

“…2 In addition, this chemical was successfully used to enhance the HCl viscosity during acid placement in horizonlly oil wells. 3 However, Polymer-based acids are not recommended to be used any more as a divertor in acidizing treatments for Saudi Aramco fields especially into low reservoir quality such as low permeability formation, due to residue effect which it might cause formation plugging. Therefore, vicoelastic surfact-based fluid is wildly used in acidizing a corabonte reservoir as a divertor fluid in both a producer and an injector wells when acid reacts with a formation leading to increase HCl viscosity solution and it can divert live acid into less permeable zones.…”

A Case Study of a Successful Matrix Acid Stimulation Treatment in Horizontal Wells Using a New Diversion Surfactant in Saudi Arabia

“…6,7 To overcome some of the problems encountered with polymer-based fluids, viscoelastic surfactant-based acid systems have been successfully used over the last few years. [8][9][10][11][12][13][14] Simple inorganic salts cause the molecules of viscoelastic surfactants to form long worm-like or rod like micelles. 15 Entanglement of these micelles generate a 3-D structure in solution which increases the viscosity of the solution.…”