Saudi Aramco experienced serious corrosion problems in oil production tubing in one offshore field, attributed to presence of H2S, CO2 and varying levels of water cut. In early 2002, the company installed on trial test basis Glass Reinforced Epoxy (GRE) or commonly known as fiberglass lined carbon steel tubing in three wells. The fiberglass lining was installed to provide a corrosion barrier to protect the steel tubing from internal corrosion. As far the technology, the fiberglass lining or sleeve is carried out joint by joint by inserting a solid fiberglass tube into the low cost carbon steel tubing and cement is pumped into the narrow annulus between the fiberglass liner and the carbon steel tubing. The connection area is protected by the combination of end flares and a corrosion barrier ring. The company examined various methods to evaluate the performance of the fiberglass lined tubing, without having to pull out the tubing from the well as these wells are oil producers. After review of the evaluation options, it was decided to run a multi finger caliper to evaluate the condition of the fiberglass lining and check for any internal corrosion in the steel tubing. The log showed the fiberglass lining to be in good condition with no damage indicating that the steel tubing was protected from corrosion. The other two wells had no tubing leaks indicating the GRE lining is providing corrosion protection. Based on successful trial test results, the company adopted the technology to protect tubing strings deployed in corrosive environments in oil producers, water injectors and water supply wells. Field experience has shown that the use of fiberglass lined tubing is a low "life cycle cost" solution compared to other options. There has been no workover in these wells since installation. Today fiberglass lined tubing is applied in Saudi Aramco in high water cut oil producers, water injectors and combined water source and injection wells. The paper shares the history of corrosion, challenges and lessons learned during the implementation of the solution, various performance assessment methods evaluated and the results and interpretation of the caliper log.
Several old wells have been successfully sidetracked and short radius horizontal holes were placed at the top of the Arab-D reservoir. The main objectives of this type of recompletion are to reduce water coning and improve the oil recovery at the water flood front. Several attempts were made to sidetrack the first well. The downhole motor failed to build the hole angle at the required buildup rate while penetrating the anhydrite formation between the base of Arab-C and the Arab-D. Hole enlargement across the anhydrite section was found to be the reason for the tool failure. Laboratory studies were carried out on anhydrite core samples taken from the base of the Arab-C section. Examination of the core samples by XRD provided detailed mineralogical composition of the rock. To determine the dissolution and erosion effect of different fluids, core plugs were hot rolled in stainless steel cages placed in steel aging cells filled with the drilling fluid samples. NaCl brine-based fluids dissolved up to 3 wt% of the rock sample and eroded additional 7 wt%. CaCl2 brine system treated with Ca(OH)2 and CaS04·2H2Oshowed no dissolution and very little erosion. Oil-based invert emulsion mud with CaCl2 brine as the internal phase showed absolutely no effect on the rock samples. A non-damaging oil-based mud formulation was developed and successfully used to sidetrack and drill several short radius wells. This paper presents the laboratory data along with the drilling and completion fluids formulations being used. Problems that were encountered during the drilling of the first well are also discussed. Introduction Many fields in Saudi Arabia produce mainly from the Arab-D carbonate reservoir which is overlaid by 100 – 170 ft of anhydrite cap rock. On top of the anhydrite lies the Arab-C which, in some areas of the field, is a water bearing and highly pressurized formation. All the field wells are initially completed open hole with the 7 in. liner set at the top of the reservoir. Two methods are used to shut off water entry and increase oil recovery from the unswept zone. In the first method, a short 4 1/2 in. liner is run and cemented across the open hole as shown in Figure-1 and the well is produced by perforating the liner across the unswept oil zones. The second method involves setting a wireline bridge plug capped with 10 ft of cement in the open hole slightly above the oil-water contact. The disadvantage of these methods is the problem of water coning. As oil production continues the water cone rises around the wellbore and as a result, the water production increases until the well dies before the oil in the unswept zone is recovered. Advances in horizontal drilling offer an alternate well completion method that can reduce water coning and increase oil recovery. The process involves cutting a window in the 7 in. casing of the existing well and drilling 500 – 1000 feet of 5 7/8 in. horizontal drain hole into the top of the reservoir as shown in Figure-2. Angle Buildup Problem Several attempts were made to sidetrack the first well as planned (Figure-3). The 100 ft and 60 ft radius motors failed to build the angle of inclination at their designed rates of 57° and 90° /100 ft respectively. The 5 7/8 in. curved hole section was drilled three times to try to place the lateral hole into the target zone. All curves were drilled in a very hard anhydrite formation, between the base of the Arab-C and the Arab-D, and there was no indication of borehole instability.
This paper describes laboratory and modeling work to utilize high-sulfate pit brine and calcium chloride solutions as a means to the permeability of water producing zones. The study included compatibility tests, coreflood experiments, and scale prediction to calculate SI and SA at surface and reservoir conditions. The pit brine contains sulfate ions at 120,250 mg/L and its TDS is nearly 400,000 mg/L. Three solutions that contained calcium chloride at 10, 20, and 30 wt% were prepared. Coreflood tests were conducted using carbonate core of 100 to 1,100 md. Tests were conduced at 200°F (reservoir temperature) and overburden pressure of 2,000 psi. Most coreflood tests were conducted at 1 cm3/min. The pressure drop across the cores was monitored during these tests. Compatibility tests indicated instantaneous precipitation of calcium sulfate when pit water and calcium chloride brines are mixed. Scale predictions are done for 10, 20 and 30 wt% CaCl2 brines with pit brine. The maximum super-saturation at 200oF for CaSO4 occurs at 45, 60 and 70 vol% of pit brine for 10, 20 and 30 wt% of CaCl2, respectively. Predicted maximum anhydrite is nearly 55, 81 and 97 g/L for the three CaCl2 brines, respectively. Coreflood tests indicated that maximum core plugging occurs when pit brines is injected into cores saturated with CaCl2 brines. The degree of core damage depends on the injection rate. Core flood results were explained in terms of thermodynamics and viscous fingering effects, which occur when a less viscous fluid displaces a more viscous fluid in porous media. Water production is a serious concern for oil and gas companies. On one hand, there is a cost required to lift this water, and to perform separation, treatment, and then disposal. In addition, water production causes scale, corrosion and emulsion problems. Therefore, every effort should be made to minimize excessive water production. Current techniques that rely on chemicals (cross-linked polymers) are expensive and in some cases these chemicals are not environmentally friendly. The technique described in this paper is simple, and utilizes simple and green chemistry. It can be used to plug water-producing zones in carbonate and sandstone reservoirs. This paper introduces a simple, effective technique that can be used to reduce the flow into high permeability zones. This technique can be used to minimize drill string sticking that occurs during drilling and reduce the amount of produced water during production Coreflood tests indicated that this technique is very effective in reducing the permeability of reservoir cores. Introduction Excessive water production causes major economic problems in terms of loss of oil production, as well as lifting, separating and disposing of large amounts of wastewaters. Produced water can be reduced or avoided by using mechanical or chemical means. Mechanical means include drilling horizontal wells, placing a liner then perforating the target zone, or using downhole separation equipment, e.g., a hydrocyclone. Selection of a specific water shut-off treatment depends on the sources of water, which include: coning, casing leaks, high permeability streaks, and natural fractures. Understanding reservoir characteristics and water movement in the reservoir are key factors that determine the success of these treatments. Another problem that is caused by the presence of high permeability zones is differential pressure sticking, which occurs during drilling across porous and permeable formations. Differential pressure sticking occurs when the drill pipe becomes stuck in the filter cake on a permeable formation during drilling. As illustrated in Fig. 1, during drilling, mud and filtrate are lost into permeable zones when the mud hydrostatic pressure in the wellbore, Ph, is greater than the formation pore pressure, P. As the filtrate is lost, the solids in the mud are deposited on the formation face as filter cake. The characteristics of the filter cake depend on the type and amount of solids present in the mud. A mud with high native solids content leaves a thick sticky filter cake, while a mud with bentonite produces a slick thin filter cake.
During the past four years Saudi Aramco has used short radius horizontal and multilateral drilling technology to increase oil recovery, productivity and injectivity of existing production and injection wells. This was achieved by(a) sidetracking oil wells with thin bypassed oil column and drilling shortradius horizontal holes at the top of the reservoir to control water coning and increase oil recovery, (b) drilling short radius horizontal holes across thin reservoirs and increase the wellbore flow area and well productivity, and (c)drilling multilateral short radius horizontal holes to increase the productivity and injectivity of existing oil and water injection wellscompleted in low permeability reservoirs. This paper presents well casehistories that describe the drilling and completion operations and compare the performances of the horizontal and conventional wells. Introduction The Arab-D is the major oil producing reservoir in the Ghawar field in SaudiAramco. The reservoir is dolomitic limestone and has a net thickness of about 250 ft. The formation porosity and permeability are highest at the top of the reservoir and decrease gradually to ± 5% and few millidarcies at the base of the reservoir. The Arab-C reservoir which lies above the Arab-D is, in someareas of the field, a water-bearing and highly pressurized reservoir. The two reservoirs are separated by 100–170 ft of anhydrite cap rock and the thin postArab-D stringer which is oil-bearing in some areas of the field as shown inFig. 1. Most wells in the field are initially completed open-hole in the Arab-Dwith the 7" liner set at the top of the reservoir. The post Arab-D stringer isnot produced in wells completed in the Arab-D reservoir. The Arab-D reservoir pressure is maintained by the injection of water on the flanks of the field. Aswater injection continues, the water cut increases until the wells can nolonger flow on their own, leaving 25–35 ft of unswept oil column at the top of the reservoir. One way to recover the unswept oil is to run and cement a 4-1/2" liner across the open hole and perforate across the unswept zone. The disadvantage of this method is the problem of water coning. As oil production from the unswept zone continues, the water cone rises around the wellbore and as a result the water production increases until the well dies before the oil in the unswept zone is recovered. Applications of Short Radius Horizontal Drilling : Short radius horizontal drilling technology was used to increase recovery of the unswept oil at the top of the Arab-D and to increase the potential of oil and water injection wells. Existing oil producers and water injection wells in the Ghawar field were reentered and short radius horizontal single and multilateral holes were drilled. This technique provided an attractive cost benefit compared to drilling new wells since the infrastructure is already inplace. Short radius horizontal completions were utilized in four major applications outlined below. Recover Unswept Oil from the Top of the Arab-D Reservoir. Many oil producers in the Ghawar field ceased to flow because of high water cuts leaving 25-35 ft of unswept oil at the top of the reservoir. Reentering the wells and drilling short radius horizontal holes across the top of the reservoir proved to be the most economical and effective way of recovering the unswept oil.
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