No abstract

Theories of failure of elastohydrodynamic lubrication are briefly reviewed, but none that relate to scuffing per se and no general criterion that accounts for the sensitivity of scuffing to rolling as well as sliding speed are found. A theoretical investigation of micro-EHL by Baglin, for surface finishes with a lay parallel to the sliding direction, predicts boundaries in the operating condition domain to a regime of mixed lubrication in which little elastic deformation of asperities by micro-EHL is expected. A new thermal model incorporating salient features of scuffing in mixed lubrication conditions is described. It is shown to give the form of a boundary in the sliding/rolling speed domain above which localized temperatures close to melting may be expected and below which lower temperatures suggest running-in without scuffing may be expected. Results of scuffing tests on circumferentially ground discs, at sliding and rolling speeds in the range 3-10 m/s, are reported and shown for surfaces with a distinguishable mainscale wavelength in their topography, (a) to provide further support for the location of the boundaries to the mixed lubrication regime in the operating domain predicted by Baglin and (b) to match the form of the thermal model in the speed domain. Implications for engineering practice are briefly discussed.

Globally, many thousands of potentially productive oil and gas wells suffer internal corrosion due to H2S, CO2, and other produced gases and liquids. This limits their capability to provide a packer sealing area suitable for traditional mechanical production packers. Total E&P Qatar planned a recompletion using intelligent well technology in a well in which they expected to find some corrosion. Before initiating the recompletion, they investigated the use of alternative packer technology. Swelling elastomer packers have been used worldwide in many applications, but verification was required in this case to assess whether such packers would hold pressure in a corroded section of casing. In addition, testing was also was needed to assess whether the completion could be pulled in the event that it became necessary to retrieve the components from the well. A swellable packer with multiple cable feed-through was designed and manufactured to approximately two-thirds size of the originally specified packer. A sample of corroded casing, supplied by Total E&P Qatar, was used to build a test jig. The jig was equipped to simulate and record pressure, temperature, and other downhole conditions. Theoretical simulations were performed to assess the force required to overcome the anchoring forces applied by the swelled elastomer and were verified by a pull test. It is expected that with a reliable sealing mechanism for these older wells, technically and financially viable workovers and re-completions can be performed, thereby extending field life and adding to recoverable reserves. This paper describes the application and test procedures along with the verification and results of the testing performed. Introduction The Al Khalij field lays 100km offshore Qatar in 60m water depth. The first discovery dates back to 1991, when the Mishrif reservoir was confirmed as oil bearing. The field was developed in a phased manner to reduce developmental risks and to optimize development cost. First production from the field was delivered in 1997. At the end of 2005, three phases of development of the field had been completed, and currently, an infill drilling program is in progress. Presently, this vast field is produced through seven unmanned wellhead platforms and one water-separation platform. A total of 37 oil producers, six water injectors, and four water producers have been drilled and completed to date. Due to the proximity of the aquifer, significant amounts of water are produced. Owing to the sub hydrostatic reservoir pressure, producer wells are equipped with Electrical Submersible Pumps (ESPs). The electrical generation necessary to power the ESPs is located on Halul Island, located 45 km away from the field as shown in Fig. 1. Most of the water produced is separated offshore on a process platform and is re-injected into the field with the water injector wells aiming at sustaining reservoir pressure. Additional water is produced from the Umm Er Radhuma shallow aquifer and re-injected into the Mishrif reservoir in order to achieve a full voidage replacement and further sustain reservoir pressure.1,2 The Mishrif carbonate reservoir is comprised of several thin stacked layers (three to five meters thick) with a wide range of permeabilities (five to 300mD). In order to increase the Productivity Index and the drainage area of the oil producer wells, they usually feature long to very long cased horizontal drains, which are among the most ambitious ones in the industry. Nearly all wells drilled after year 2000 feature drain lengths in excess of 2000m (see Fig. 2).

Twin-disc tests in microelastohydrodynamic lubrication (micro-EHL) confirm that prior running-in at lower sliding speed enhances load and temperature at scuffing. Examination of surface oxidation and smoothing gives a new insight into the running-in process and suggests that the latter is the dominant effect. Restatement of the operating conditions in terms of non-dimensional groups that take into account the current roughness of the surfaces shows there to be little difference at scuffing.

More than two-thirds of the world's oil and gas is currently being produced from mature fields, and although new prospects continue to be discovered, the industry is realizing that the older finds, now mature, are significantly larger than originally thought. Therefore, much of the world's future oil and gas production will continue to depend on brownfield production. Traditionally, when wells in these fields started to show production declines, operators often chose to abandon them rather than consider rework operations, since most production declines resulted from difficult-to-remediate unwanted water or gas production. In addition to water and gas influx, many fields had less-than-ideal production environments that contained CO2 and H2S, causing corrosion of tubulars. Realization of the need to revisit mature-field production has encouraged new technologies and remedial options to be developed. One of the recently proven technologies, swellable-elastomer packers, has enabled successful workovers, sidetracks, and re-drills that might otherwise have been too difficult, unreliable, or too expensive to be performed a few years ago. The packer uses the swelling properties of rubber in hydrocarbon or water to expand so that the annulus around the pipe is sealed. This capability has proved to be a great advantage in older wells where corroded, pitted and otherwise irregular surfaces in addition to reduced wall thicknesses due to corrosion make setting and sealing of conventional packers very difficult. This paper provides case histories and applications of swellable straddles and plugs in openhole and cased-hole scenarios that have enabled shut-in wells to be placed back into production. The discussion will include coiled-tubing tool and wireline deployment methods, wells in which swellable packers have been run as part of the completion string, and testing of swellable packers that provided seals in corroded casing. The principles and techniques involved are applicable to brownfield situations worldwide. Introduction Since the introduction of swellable elastomer units approximately 10 years ago, approximately 20,000 of these units have been delivered to operators worldwide. Since then, the scope of possible applications has increased constantly as new ideas, trials, and technological advances have been introduced. Swellable-elastomer packers are run in both open- and cased-hole wellbores, in extended-reach-drilling (ERD) wells, in multilateral (MLT) wells; with feed-through in conjunction with intelligent completions, in hydraulically fractured wells, in combination with cement, and in producers and injectors in low-temperature to high-temperature/high pressure (HT/HP) fields.