Unconventional gas reservoirs, including tight gas, shale gas and coalbed methane, are becoming a critically important component of the current and future gas supply. However, these reservoirs often present unique stimulation challenges. The use of water-based fracturing fluids in low permeability reservoirs may result in loss of effective frac half-length caused by phase trapping associated with the retention of the introduced water into the formation. This problem is increased by the water-wet nature of most tight gas reservoirs (where no initial liquid hydrocarbon saturation is, or ever has been, present) because of the strong spreading coefficient of water in such a situation. The retention of increased water saturation in the pore system can restrict the flow of produced gaseous hydrocarbons such as methane. Capillary pressures of 10 to 20 MPa or higher can be present in low permeability formations at low water saturation levels. The inability to generate sufficient capillary drawdown force using the natural reservoir drawdown pressure can result in extended fluid recovery times, or permanent loss of effective fracture half-length. Furthermore, use of water in subnormally saturated reservoirs may also reduce permeability and associated gas flow through a permanent increase in water saturation of the reservoir. Secondary costs, such as rig time for swabbing, can add to the negative economic impact. Gelled liquid petroleum gas-based fracturing fluids are designed to address phase trapping concerns by replacement of water with a mixture of liquid petroleum gas (LPG) and a volatile hydrocarbon fluid. Once the well is drawn down for flowback, some of the LPG portion of the fluid may be produced back as a gas, dependent upon temperature and pressure. The remaining LPG remains dissolved in the hydrocarbon fluid and is produced back as a miscible mixture using a methane drive mechanism. By eliminating water and having LPG as up to 80 - 90% of the total fluid system, cleanup is greatly facilitated, even in wells having very low permeability and reservoir pressure. The effects of fracturing fluid retention on gas flow in the fracture face can be as important as fracture conductivity when designing a treatment. It is possible to have a conductive fracture with good half-length in the desired productive zone and still not realize economic or optimum gas production if phase trapping and/or relative permeability effects are restricting gas flow. Description Gelled LPG-based fracturing fluids are a unique hydrocarbon-based fracturing fluid system designed for gas well stimulation. They use up to 100% gelled LPG for the pad and flush. The sand slurry stages use a mixture of up to 90% LPG with the balance of the volume being a volatile hydrocarbon-based fluid. All chemicals and proppant are added to the base fluid at the blender. LPG, which composes the balance of the downhole fluid volume, is injected at the wellhead where it forms one miscible mixture with the base oil. It is important to note that under pumping pressures, this is a single-phase gelled fluid system, similar to gelled oil in rheology, friction pressures, proppant transport and leakoff control.

This paper represents a case history covering a span of 4 years during which personnel were recruited, trained and developed to staff a very large offshore drilling operation in a relatively new area starting in 1972. Included in the paper are so:me details of the reasons why certain groups of personnel were selected and how they were placed into the overall operational framework of big, semisubmersible drilling rig operations. A description of the training center is included as well as how it was used to carry out the development program for personnel at all levels.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper is a follow-on to SPE 28694 (Ref. 180) which summarizes and categorizes ESP literature by a number of different topics. The intent is to list problems mentioned in various papers and a quick mention of the solutions, which are discussed in the given references. As mentioned in the previous reference, it is also an attempt to relate problems to various field conditions, however many of the field papers do not include a complete listing of field conditions, so to be able to do this from using the literature is often not possible.

On the northwestern coast of Peru, the International Petroleum Co., Ltd., initiated sand-oil fracturing in late 1953. As of May 31,1955,319 jobs had been performed in 61 of the 71 producing pools and in all eight of the producing formations. The wells treated have thick producing sections completed through gun-perforated casing, perforated liners, or combination strings.In the average treatment 300 bbl of refined oil was used to carry 18,900 lb of Ottawa sand; in most cases, the sand-oil mix was injected down the annular space. A bout 50 per cent of the jobs were done in wells where a thick series of sands and shales were exposed.Of the 319 jobs done, 70 per cent (or 271 jobs) were successful; the total additional oil produced of May 31, 1955, was 1,860,633 bbl and at that time additional oil was still being produced at the rate of 5,419 BOPD. Only the six most important producing sands are discussed in the paper. In one of these (Lower Parinas sand) a comparison was made between the results of nitroshooting and sand-oil fracturing. Composite production curves and typical electrical log sections are shown for each of the six sands. Also a statistical summary of results from all eight formations is presented.Variables which might have affected the success of treatments were investigated empirically and theoretically, but no satisfactory means 12 of predicting results of sand-oil fracturing was found. It was noted, however, that the beneficial effects were divided into three categories: induced fractures, elimination of well damage, and opening new reservoirs. The general conclusions were that sandoil fracturing was successful in wells where as much as 75 per cent of the exposed formation was shale, in old, apparently depleted wells, and that opening new reservoirs plus the elimination of well damage were important factors in the successes.

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