Rotating Jetting Nozzle Adds Value in the Cleanup of Horizontally Gravel Packed Well-Case Histories from Sandstone Environment
Abstract: TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA 360-degree rotating jetting tool has been successfully deployed to cleanup about 1000 ft of 6.25" horizontal openhole gravel packed (OHGP) well. The exercise was carried out using Nitrified 10% HCl placed from the toe to the heel at Coil Tubing average rate of 20 ft/min. Three passes were made at total fluids rate of 1.0 bpm. During the fluid placement, no losses were encountered. After the treatment and initial production testing, a baseline memory product… Show more
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Cited by 5 publications
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A New Approach to Matrix Sandstone Acidizing Using a Single-Step HF System: A Niger Delta Case Study
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe use of unique or modified HF acid systems for matrix acidizing within the Niger Delta and some other parts of the world is still the preferred method for effective stimulation of sandstone reservoirs. The continued success of treatments done with modified HF systems in this area are due to its ability to mitigate the rapid spending of the active acid with clays and silicates; prevent matrix unconsolidation in the near wellbore region and the subsequent precipitation of acid reaction by-products within specific well applications. This success has brought about modifications to the acid system and new applications for various well scenarios. This paper discusses the successful application of a unique sandstone acidizing process that uses a single acid stage (no preflush or postflush is required) making multiple stage treatments much simpler while still achieving both economic and technical targets for the well. It covers the non-formation stimulation treatment of several wells using this single-step method and also describes a successful approach to improving the productivity of high water cut wells with severe finesdamaged gravel packs by this system. Unique experiences acquired during the field trials carried out within the Niger Delta using this system are evaluated. The results demonstrate a significant increase in incremental hydrocarbon production for normally high risk, low reward wells and remarkable stimulation cost reduction via reduced chemical volumes, less equipment requirements and shorter job times.Also included are a thorough analysis of actual candidate selection criteria, fluid chemistry, actual job design and operational issues during execution of treatments. Key technical and economical performance indicators including skin factors, production rates, specific productivity indices, treatment costs indicate that this system has certainly and successfully increased the application envelope for unique HF treatments within sandstone reservoirs.
A New Approach to Matrix Sandstone Acidizing Using a Single-Step HF System: A Niger Delta Case Study
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe use of unique or modified HF acid systems for matrix acidizing within the Niger Delta and some other parts of the world is still the preferred method for effective stimulation of sandstone reservoirs. The continued success of treatments done with modified HF systems in this area are due to its ability to mitigate the rapid spending of the active acid with clays and silicates; prevent matrix unconsolidation in the near wellbore region and the subsequent precipitation of acid reaction by-products within specific well applications. This success has brought about modifications to the acid system and new applications for various well scenarios. This paper discusses the successful application of a unique sandstone acidizing process that uses a single acid stage (no preflush or postflush is required) making multiple stage treatments much simpler while still achieving both economic and technical targets for the well. It covers the non-formation stimulation treatment of several wells using this single-step method and also describes a successful approach to improving the productivity of high water cut wells with severe finesdamaged gravel packs by this system. Unique experiences acquired during the field trials carried out within the Niger Delta using this system are evaluated. The results demonstrate a significant increase in incremental hydrocarbon production for normally high risk, low reward wells and remarkable stimulation cost reduction via reduced chemical volumes, less equipment requirements and shorter job times.Also included are a thorough analysis of actual candidate selection criteria, fluid chemistry, actual job design and operational issues during execution of treatments. Key technical and economical performance indicators including skin factors, production rates, specific productivity indices, treatment costs indicate that this system has certainly and successfully increased the application envelope for unique HF treatments within sandstone reservoirs.
Horizontal Openhole Gravel Packing in a Depleted and Heterogeneous Reservoir
Open-hole gravel packing in vertical/conventional wells is an accepted sand exclusion method that has not gained wide and rapid application in horizontal wells. The reason is largely due to sand placement challenges in the horizontal drain that could lead to premature sand screen-out. Consequently, many operators are skeptical gravel packing horizontal wells since failure could probably result in enormous capital risk. In the Niger Delta, about 70 % of the hydrocarbon-bearing reserves lie in shallow unconsolidated reservoirs where the sonic transit time vary between 110 to 140 us/ft. Production from these intervals has proven record of sand threats to operating cost, well integrity, surface facilities and production sustenance. The challenge is to complete wells in these reservoirs with sand exclusion materials that would guarantee full life-cycle production performance. Early horizontal wells in the region were completed with stand-alone screens, but recently, the expandable sand screen (ESS) took a leading edge. Though the ESS has a higher inflow area compared to other screens, its high cost, lack of full-bore expansion and the required lead-time continue to raise concerns especially when considered for applications in brown field development where well potential and reserve rewards are low. In response to these concerns, in 2002, openhole gravel packing (OHGP) in a horizontal well was investigated and considered as an alternative sand exclusion option in Shell Petroleum Development Company (SPDC). The trial candidate, the Obigbo-North QWSB-3 was selected and successfully completed as the first horizontal OHGP in SPDC using the alpha-beta wave concept. Based on simulation results, about 9237 lbm of sand was planned for placement in 1000-ft of 6.0-in hole size, however, the actual sand pumped was about 10830 lbm. This represents an estimate of 6.25-in drain hole size. The application saved over $0.3 million when compared to the cost of using ESS. For the Eastern asset team that drills an average of 12 wells annually, an annual projected completion cost-saving of some $3.6 million is achievable. Based on the initial production testing, Obigbo-North Well QWSB-3 tested 3250 BOPD with a productivity index (PI) of 130 bbl/(psi-D). Baseline Memory Production Logging Tool (MPLT) logging showed that the entire drain section completed on the clean sand member had effective inflow into the linerbore. In addition to establishing confidence in the application and performance efficacy of OHGP, this trial and the significant cost-savings will engender a paradigm shift to horizontal well sand control. In this presentation, we will share some data and results based on field experiences, challenges and new understanding. Introduction This paper discusses the first application of horizontal open hole gravel packing as a sand control method in SPDC. The paper further demonstrates the evaluation of the inflow profile (based on memory production log) as a yardstick for determining the completion efficiency, and reveals the economic argument against using ESS as seen in Well QWSB-3 (figure-1) located in the Obigbo-North field of Niger Delta, Nigeria (figure-2). Production "hot-spot-effects" a phenomenon characterized by massive inflow into the liner-bore at a particular point (figures-3–5) is a common phenomenon in horizontal wells completed with stand-alone screens and ESS (that are not fully expanded to the sand-face). The problem is attributed to differential plugging of the completion screen by the migrating formation fines and/or improper horizontal drain section clean out2,3,4. When a stand-alone screen is partially plugged, the resultant annular flow converges to a point where intense inflow into the liner-bore is observed. This problem leads to higher drawdown, liner erosion, sand failure and ultimately production decline1,10. These problems commonly associated with wells completed with stand-alone screens, led to the many recent applications of ESS by the SPDC Land Asset Team. However, high material installation cost and complete expansion remain key challenges in ESS applications. SPDC decided to try horizontal OHGP as an alternative sand exclusion option that will be cost-effective and capable of sustaining production. Consequently, a trial application was executed at the end of the second quarter of 2002 in Obigbo-North Well QWSB-3. The well was planned to develop some 8.5 Million STB from the D3.200A reservoir at an initial offtake rate of 3000 BOPD (tables-1,2).
Phosphonic Acid Complex for Stimulating HF-Sensitive Reservoirs – A Revolutionary Response
HF-sensitive reservoirs that could not be hydraulically fractured nor effectively stimulated have been a challenge to the Petroleum Industry, hence locking the potential reserves that could otherwise be producible. These formations are typically those with high swelling clays, chlorite clays, feldspars and certain zeolites. Experience shows that even when such formations are stimulated with conventional HF- or HCl-based acid systems, the production performance declines shortly after the treatments, causing the reservoirs to produce at less-than-optimum rates. The skin damage associated with such reservoirs and stimulation by-products act as down-hole chokes, strangling production and increase drawdown. Successful stimulation of these kinds of HF-sensitive reservoirs had been carried out with a Organo-Phosphonic Acid Complex. Treatments have been carried out in seven Oil Producers, Water Injectors and Gas Injection wells in the Niger-Delta Nigeria and an oil producer in South East Asia. Post-treatment rates were above 800% of the pre-treatment values and more than 100% the maximum potentials ever recorded by most of these wells since they were commissioned. The new acid system offered true stimulation of carbonate and sandstone reservoirs as well as restoration to natural permeabilities of these intervals by the process of sequestration and complexation. An overall dramatic response of more than 200% over the wells treated with other formulations in the same basin was achieved. This paper discusses the non-HF based Organo-phosphonic acid formulations for Oil Producers, Gas Producers, Water Injectors and Gas Injection wells in both carbonate and sandstone reservoirs. The process of dissolution of the acid soluble and insoluble minerals that plug the near-wellbore region; candidate selection criteria; design; process of scale inhibition; field applications; results; treatment effectiveness and evaluations. The performance over other formulations is compared with respect to treatment costs, accelerated production, payback time, sustained production or Injectivity after treatment and percentage of original permeabilities being restored. Introduction The world's crude oil and gas come from limestone (CaCO3) / dolomite (CaMg[CO3]2) - Carbonate formations and quartz particles / Silicon dioxide (SiO2) - Sandstone formations. The carbonate formations could be found in their pure forms or in the form of carbonate or siliceous sands cemented together with calcareous materials whereas most sandstone formations are found in the form of quartz particles / silicon dioxide bonded together by various kinds of cementing materials, chiefly carbonates, silica and clays. Primarily, limestone and dolomite react at high rates with hydrochloric acid (HCl) and moderately with formic and acetic acids but sandstone reacts very little. The amount of reaction of these acids in sandstone formations depends on the amount of calcareous materials present. However, the silicon dioxide, clay and silt react with hydroflouric acid (HF). Since HF reacts with silt, clay, sandstone and most drilling fluids, it has been found effective in removing impairments and stimulation of sandstone reservoirs. The major defects of HF is the formation of by-products of calcium fluoride (CaF2) with calcareous material and sodium hexafluorosilicate (Na2SiF6), hydrated silica (SiO2·2H2O) and potassium hexafluorosilicate (K2SiF6) which are both insoluble and damaging precipitates. Carbonates, clays and iron compounds can ruin a well executed treatment. The chemistry of the reactions leading to the above insoluble and damaging precipitates are shown in appendix A. Fluorine is a very reactive element and since the composition of sandstone is varied, many reaction products can form when sandstone formations are stimulated with HF acid, hence HF-sensitive reservoirs that could not be hydraulically fractured nor effectively stimulated had been left unattended, thereby leaving the wells to produce at less-than-optimum potentials. Such reservoirs are predominantly made up of high swelling clays, feldspars, chlorite clays and certain zeolites.
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