TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA survey of cement manufacturers in the Asia Pacific Region revealed that only five companies produce a certified API Class G cement. Because of this, certain countries have been forced to import cement and in many cases ship it great distances. In some situations, API Class G cement can cost three times more than local construction cement. While the authors believe that the API Monogram is an excellent benchmark for oilwell cement, the question is -is it necessary to preclude good local cements from use simply because they are not certified. After all, the key issues for oilwell cement are predictability and performance, not certification In the absence of local API Class G cement, the authors propose two ways to use local cement in oilwell applications. First, work with existing construction cement companies to develop cements that consistently meet specifications of the desired API Class and use it in the field. Second, when and where it is applicable, use construction cement for oilwell cementing. The authors are implementing both techniques successfully in parts of South East Asia. This paper presents historical and technical background as well as laboratory data to support the use of local cements as an alternative to imported API Class G cement. Also, presented are several case studies on the use of local cement in oilwell applications as a means to save drilling costs.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIt is well known that increasing the ionic strength of aqueous solutions containing certain categories of anionic surfactant can produce interesting behaviors. The molecules of some surfactants cluster together forming spherical micelles. However, a select few surfactants, with particular molecular structure, undergo a remarkable transition from spherical micelles to larger, anisometric aggregates. The size, flexibility and extent of interaction of these aggregates all have an influence on the rheological properties of such solutions, producing very substantial viscosities at low shear rates.Conversely, when these surfactant solutions encounter other chemical species, particularly relatively non-polar materials, like alcohols, glycols and hydrocarbons, this affects the shape and structure of the micelles. As a result, the phase behavior is altered and the solution undergoes a dramatic reduction in viscosity.Proper selection of a surfactant allows its application in several oil field treatments such as reservoir gravel packing, frac-packing, fracturing, brine thickening, non-damaging temporary plugs and also for reservoir flooding and water shut-off.The main advantage of these solutions, compared to conventional polymer systems, is the potential for reduced formation and proppant pack damage. However, there are many other advantages. These fluids exhibit unexpectedly low high-shear viscosities resulting in low friction pressures, even in small tubular. In addition, due to the very low viscosity of the broken fluid, faster load recovery of injected fluids is possible. A final benefit offered by these systems is operational simplicity at the well site, since there is no need to "pre-gel" tanks ahead of the treatment. This paper describes the chemistry involved to develop these viscous solutions and their applications in different treatments in the field.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn the past few years, oil companies have ventured more frequently into deepwater areas in the search for hydrocarbons. This trend is likely to continue, or even accelerate, in the next few years and, if anything, we are likely to see ever-greater water depths. There are several aspects of deepwater wells that make them particularly challenging, from an engineering perspective, through all phases of the process -construction, production, intervention and abandonment. This paper, however, focuses on the issues surrounding deepwater well cementing, primarily during the well construction phase.This has been an area of intense interest in recent years, due to industry realisation that the deepwater environment had one or two surprises for drillers. Most notable amongst these is the problem of shallow water flows that can easily wash out the weak, unconsolidated sediments, resulting in seabed subsidence and loss of the hole. Other issues include the presence of shallow gas and gas hydrates, strong subsea currents and extremely low fracture gradients, with the everpresent risk of lost circulation or wellbore collapse. The low seabed temperature, which can be below freezing, also depresses the normal geothermal gradient to a variable depth, depending on the thermal properties of the strata.None of this is good news for cement, which is required to have short thickening time, rapid development of mechanical properties, a fast liquid:solid transition and low permeability to provide casing support, cope with the risk of influx and provide a long term hydraulic seal, amongst other things. This has driven the development and marketing of a host of proprietary cementing systems that claim to address some, or all, of these problems. This paper reviews the deepwater cementing issues, in detail, and examines the physical and mechanical properties of various cement systems to assess which parameters are truly critical to success. It combines laboratory data with field case histories and working practices in several parts of the world, to help engineers decide on the best formulations for cementing deepwater wells.
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