Cementing gas wells in coalbed methane (CBM) formations can present a cement-circulation challenge because the coal formations tend to have low fracture gradients and break down under the hydrostatic pressure of the cement column. The use of conventional lightweight cement slurries and/or foam cement significantly increases the prospect of maintaining circulation throughout cement placement. However, wells with exceedingly low fracture gradients can suffer either partial or complete loss of circulation during cement placement even with lightweight slurries. Both conventional lightweight cement slurries and foam cements have restrictions. Conventional lightweight cement systems use low-density materials (i.e. hollow spheres, gilsonite) and high water-to-cement ratios as a means of reducing the equivalent circulating density (ECD). The lightweight materials and high water requirements detract from the compressive strength of the cement, thereby limiting ultra-low densities while achieving adequate compressive strength. For foamed cement, the gas-to-slurry ratio should stay within a specific range to help ensure optimal cement properties; otherwise, the set cement could become permeable. This requirement has led to the hybridization of two systems to create an effective cementing solution. By combining the two systems, the best attributes of both can be captured. Starting with a lightweight cement system provides a low base-slurry density that allows the gas to be added to lower the density further while maintaining the compressive strength and foam stability. This paper discusses an operator's challenge and the use of the above solution to cement wells in the Western Canada Sedimentary Basin (WCSB) across CBM formations. Introduction Cementing CBM wells usually requires a cementing system that reduces the risk of lost circulation, while providing excellent annular displacement efficiency with the aim of achieving 100% annular fill. When set, the cement should give complete zonal isolation for the life of the well (stimulation, production, and selective workover) while providing lateral pipe support to combat compaction-induced failures. Foamed cement has historically fulfilled these requirements.[1] Table 1 summarizes required cement properties. Foam cement offers many advantages, including the following:Low hydrostatic pressure. Circulation losses while drilling and completing in CBM fields are common. A reduction of cement density from 1920 to 1440 kg/m[3] (16.0 to 12.0 lb/gal) can reduce the hydrostatic pressure in a typical WCSB well by ~5.5 MPa, or 400 psi.Dynamic control of losses. The thixotropic and expansive nature of foam, together with the structural features of the bubble cells, helps reduce losses to vuggy or fractured formations and helps reduce fluid loss to permeable formations.Strength-to-density ratio. Foamed-cement slurries can yield higher strengths than low-density slurries extended by adding water only.Mechanical properties of set cement. The high ductility and bubble structure of foamed cements has been shown to be beneficial when the cemented annulus is subjected to thermal and mechanical loading. These features of foamed cements can enable internal deformation without cracking.[2–4]Hole cleaning. The high apparent viscosity of foamed fluids can enable them to exceed the shear stress required to mobilize highly gelled muds and to exhibit superior solids-carrying capability.[5–7]Improved mud displacement, expansion properties, and fluid loss.[8] Foamed-cement slurries are considered to have superior mud-removal properties and the capability of filling lost-circulation voids. The two phases of foamed cement lower the overall slurry fluid loss, which is known to be one of the primary properties for controlling gas and fluid influx into the setting cement.[9–13]

There are a number of challenges associated with setting cement plugs in an openhole well. Most importantly, drillpipe can become differentially stuck across a lost-circulation zone, and the plug may become contaminated with the intermixing of the mud resulting in inadequate isolation or insufficient strength.Cement plugs are used for various reasons including healing losses, abandonment, and directional drilling. It is essential to these operations that a competent cement plug is placed the first time. The value of placing the designed cement plug properly is measured by non-productive rig time, wasted material, and additional cementing services.An innovative tool and a special process 1 were designed to meet the challenges associated with setting cement plugs. The tool connects sacrificial/drillable tubing to the drillpipe and allows an operator to trip into the well and spot the cement plug across the problematic zone. Once cement is placed, the tool is disengaged and the operator trips the drillpipe out of the hole, leaving the cement plug and tubing undisturbed. The sacrificial tubing is drillable; therefore, the operator can drill through the plug or commence other operations as required.This paper discusses the challenges operators face when setting cement plugs and how the risk and non-productive time are reduced with this innovative plug-setting process and tool. Well examples are documented from case histories to illustrate the success and lessons learned.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling in the Arctic can present a number of challenges even before the drilling begins. Among the challenges are logistic difficulties, weather extremes, and environmental sensitivities. To offset the production decline for natural gas in North America operators must confront these challenges by resuming exploration in the Arctic.The target in this case study is a well in the Paktoa field. The design challenge presented by this well was to drill the well to total depth (TD) with the lowest number of casing strings while avoiding remedial cementing operations. Given that the mud-weight window predicted for this wellbore was quite narrow, well planners determined that no fewer than five casing strings were needed to reach TD. Multiple casing strings can lead to tighter annuli and more challenging cementing operations.Using modeling software as an aid to cement design, planners determined that the cement on the first liner, from 1,300 to 2,600 ft, could not be circulated conventionally without breaking down the formation because of the high equivalent circulating density (ECD). The greatest contributor to the high ECD is the tight annulus of the liner lap. The model parameters were reversed and the model predicted that a reverse-circulation cementing (RCC) operation would be successful.RCC is a method of pumping cement down the annulus and receiving returns inside the casing. One advantage of reverse circulating is that the ECD is reduced and less pressure is exerted on the formation. This will help reduce or eliminate cement losses into weak formations.Placing the cement down the annulus appeared to be feasible with the computer model but to conduct the operation in the field, other challenges were addressed. In a reverse operation, the float valve is removed or sheared out before pumping cement. This is not of concern with a normal casing * Formerly employed by Devon-Canada

The large Alberta's heavy oil and bitumen reserves demand novel, cost effective upgrading schemes for distillates production and resids disposal. Vacuum resids (VR's 500ºC+) in average comprise 50 % (w/w) of these reserves. This study presents a new alternative for upgrading VR's by combining three processing steps: I. Production of modified almost instable heavy molecules by mild thermal cracking (Visbreaking, VB), II. Adsorption of modified heavy molecules over inexpensive, tailor-designed porous sorbents/catalysts, III Production of hydrogen via Low temperature Catalytic Steam Gasification (CSG) of the previously adsorbed molecules. Results will be presented on the combined processing as well as using both a model molecule and real feedstock (Athabasca VR) for the adsorption and hydrogen production steps.

Many services on drilling rigs collect data electronically.