fax 01-972-952-9435.References at the end of the paper. AbstractBecause of the instability of the oil industry, operators must continually investigate new techniques and equipment to reduce operational costs. This paper will discuss four case histories involving an innovative well-intervention technique in which a coiled tubing unit (CTU) was used to deploy and set bridge plugs for plug-and-abandonment operations in geothermal wells. By using specially designed coiled-tubing (CT) tools, operators eliminated rig time and formation cooling time, thus reducing operational costs. When job designers assessed the job requirements and service options, they considered the following factors:In geothermal fields, pumping into a well to perform a kill operation for plug-and-abandonment techniques (required for conventional rig equipment) can affect the production of neighboring wells.Bradenhead pumping or pumping from the surface into a well for a kill operation is not always possible unless a kill string or workstring is deployed to a certain depth.The expense of rig time and production loss can affect operational costs. Coiled tubing has been widely used in the oilfield industry because of its versatility and economy. When CT was first introduced, its primary advantage was that it could perform operations faster than a rig because of its increased pipe-moving capability. CT is now recognized for its capability to perform services with the wellbore in an underbalanced state. Specific tools that have been developed for CT operations have sup-ported the increased scope of applications and have increased operational safety and reliability.In the case histories presented, CT was used under live well conditions to deploy and set up 13 3 /8-in. bridge plugs for plugand-abandonment procedures. Pressure-operated setting tools allowed entry into these geothermal wells under flowing conditions and allowed operators to successfully set drillable packer mandrels that have bridge plugs installed. This paper will discuss the operation of setting tools, procedures for running the plugs, and obstacles that must be considered for operators to perform a successful plug-and-abandonment operation.
A new retarded clay-dissolving system has been developed for stimulating fluid production from clay damaged sandstone formations. This system utilizes the ion-exchange properties of clay minerals to generate in-situ hydrofluoric arid on the clay mineral surfaces. Fluid properties and job designs eve discussed for this process, which has been used in over 200 treatments. In addition, production data are presented for selected treatments to show common presented for selected treatments to show common applications. Introduction Matrix acidizing treatments in sandstone reservoirs with solutions containing hydrofluoric acid are routinely performed to help remove clay damage and, thereby, improve production. This technique is especially useful in treating loosely consolidated sandstone formations where hydraulic fracturing may not be feasible. Matrix acidizing involves pumping acid, at pressures less than the formation fracturing pressure, pressures less than the formation fracturing pressure, into the porosity of the rock. This acid contacts a large surface area of rock and thereby is spent very rapidly. Studies have shown that the depth of penetration of unreacted hydrofluoric acid is penetration of unreacted hydrofluoric acid is primarily dependent on the clay content of the primarily dependent on the clay content of the formation, although only limited penetration can be achieved even in the absence of clay. For a typical sandstone formation containing 10-percent clay, the theoretical penetration radius of unreacted 3-percent hydrofluoric acid is about 6 in. Consequently, clay minerals at depths greater than 6 in. from the wellbore are difficult to remove with hydrofluoric acid. Sequential injection of a hydrochloric-acid solution followed by a solution containing fluoride ion is a new method for generating in-sits hydrofluoric acid. This will be referred to hereafter as SHF. This process will react with and dissolve clays deeper than is presently possible with conventional hydrofluoric acid. This paper will discuss the mechanism of this process as well as job design and field results. SEQUENTIAL HF PROCESS (SHF) The SHF process utilizes the ion-exchange properties of clay minerals to generate hydrofluoric properties of clay minerals to generate hydrofluoric acid on the clay particle in-situ. In practice, a solution of hydrochloric acid containing no fluoride ion is pumped into the formation. This acid solution will contact the clays in the rock and exchange protons (H+) for the cations natural to the clay protons (H+) for the cations natural to the clay minerals. The clay is now converted to an acidic clay particle as shown in Fig. 1. Next, a neutral or slightly basic solution of fluoride ion is pumped into the formation. This solution will contact acidic clay particles and combine with protons previously adsorbed to generate hydrofluoric acid on the clay minerals. In addition, some anion exchange will occur whereby fluoride ions (F-) will substitute for the anions natural to the clays. The hydrofluoric acid that is generated rapidly reacts with and dissolves a portion of the clay as shown in Fig. 1. The sequential injection of a hydrochloric-acid solution followed by a fluoride-ion solution is repeated as many times as necessary to obtain the desired penetration of hydrofluoric acid. Since hydrofluoric acid is not formed until both solutions have contacted the clay minerals, the depth of penetration is mainly dependent on the volume and penetration is mainly dependent on the volume and strength of the acid and fluoride-ion solutions. Clays are the primary minerals present in a sandstone formation which exhibit ion-exchange properties, and the SHF process will react primarily properties, and the SHF process will react primarily with these materials. In a clay-damaged formation, this is ideal since little of the hydrofluoric acid is wasted by dissolving sand.
When Petronas Carigali, the national oil company of Malaysia, planned the development of its platform EWDP-A offshore Sabah, they did so on the basis of using coiled tubing for any thru-tubing workover operations which were needed while the drilling rig was still in place. In this way the drilling rig could be fully utilized for drilling operations, thus maximizing the efficiency of, and minimizing the total time for, the development. Well EW 117 was completed on this platform as a level 6 Multilateral in July 2000 with dual 3-1/2" tubing strings accessing two laterals with measured depths of 14,910ft. and 15,236ft., respectively. The clean-out and perforation operations commenced with coiled tubing with the rig assisting. However, due to a combination of the tortuosity and the lengthy horizontal sections of the laterals, it was not possible to reach bottom with coiled tubing because of the high frictional forces encountered. After consideration of several alternatives a feasibility study was undertaken to explore the possibility of using a Hydraulic Workover (Snubbing) unit to perform the -thru-tubing operations concurrent with the continuing drilling activity. The study concluded that, with some custom designed handling equipment, a special tapered workstring and strict adherence to a permissible concurrent activity matrix, this approach was indeed feasible. The operation was performed in February 2001 and the well made available for production by the beginning of March. Throughout the workover operation the drilling rig sequence remained in accordance with plans, apart from a period of 14 hours downtime while moving the Snubbing unit into its working location. This paper will review the problem encountered, the motive forces applicable, the feasibility study and the resultant custom designed equipment and workover operation. It will discuss on the integrated team approach and detailed planning, in which active participation from Petronas Carigali, the drilling contractor and several service companies resulted in a successful operation. Introduction It has become common practice in land based development of oil and gas projects to release the drilling rig once the production casing has been set. This allows the well to be completed, perforated, tested, etc using a simple workover unit which is considerably less expensive to operate, thus leading to improvements in the economics of the process. Extending this practice to offshore development projects from fixed platforms is more of a challenge due to the constraints placed on operations by the considerations of platform space and load limitations. Nevertheless there is always a strong economic justification for keeping the drilling rig employed as much as possible in drilling operations and for planning projects to encompass concurrent drilling, workover and production efforts. By doing so the following basic advantages can be realized:Using the drilling rig solely for drilling operations reduces the overall time that it will be used in the development with consequent major economic impact on the total project costs.Producing while drilling provides for a positive contribution to cash flow and early return on investment, which are often critical considerations when project development is being considered.The ability to workover wells while drilling continues provides for added capability to perform remedial work and thereby maintain production.
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