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The production of natural gas from coal seam reservoirs follows a succession of stages that are well established and understood. Salient components are the execution of hydraulic fractures, dewatering of both native and introduced water, and the subsequent production of what it is almost entirely methane. Most coal seams are of relatively small net pay thickness and in many cases also of low permeability, i.e. 2 md or less. Produced gas comes from a combination of both free gas in the coal porosity and, especially, desorbing gas. Because of large heterogeneities and major differences among coal seam reservoirs, the hydraulic fracturing is rarely uneventful with a large number of issues to be resolved, such as fluid selection or the mass of proppant. Most of these decisions are local and often conclusion cannot be drawn from elsewhere. Frequently, a well is subjected to multiple stages of hydraulic fracture treatments. Production performance characteristics also vary considerably. The interaction between permeability, natural cleat networks and natural and artificial fractures is often complicated and difficult to predict. This results in different periods of post-treatment de-watering, the volume of water that is produced and the onset of predominant natural gas production. We have constructed a realistic physical and economic model where the NPV criterion is used to identify successful or potentially uneconomic candidates. We forecast fractured well performance using the Unified Fracture Design (UFD) approach and we account for time of de-watering and the cost of water management. Charged against the net present value of the revenue are the costs of fracturing and well completion. Five wells with different Langmuir isotherm parameters were considered for the NPV parametric studies. The parametric studies include a range of reservoir permeabilities, porosities, proppant masses, and fracture heights. The results show the window of attractive prospects and delineate the unattractive prospects which can be considerable.

Casing drilling can be an effective method of reducing drilling costs and minimising drilling problems but its uptake around the world has been slow with only a few wells drilled so far with casing. Complex geological features like the high overburden on top of shallow unconsolidated reservoirs characteristic of offshore West Africa can benefit from casing drilling when effectively combined with Managed Pressure Drilling technique. For the industry to develop a managed pressure drilling capability that will allow today’s generation of complex wells to be drilled safely with casing, it is necessary to develop models that include the effect of eccentricity , rotation and fluid rheology at bottom hole conditions on flow and pressure regimes, and to embed these models within an easy to use, intuitive well design package for pre planning and as a real time tool to monitor and provide forward simulations based on real time rig and downhole data. The paper presents new results of the theoretical predictions of the wellbore pressure regimes incurred when different types of drilling fluid flows in concentric and eccentric horizontal annuli. The concentric and eccentric casing drilling results are compared with parallel predictions from conventional drillstring results from developed analytical solutions integrated into the VisWELL(DeskTop Simulator) , which is used in simulating well operations.

Hydraulic fracturing, which has had a long and well established place in petroleum production engineering, especially in the mature areas of North America, has emerged recently with equally large role to play in China. Tight reservoirs including shale gas have promoted Chinese fracturing activities to ever higher levels. Western design and execution techniques have been adopted and modified.We present field examples for the Shun 9, a low-permeability oil reservoir (permeability ranges from 0.001 to 0.1 md) in North-Western China for which horizontal wells with multiple fractures appear to be the only choice for some credible production. The physical optimization in this work is done with the Unified Fracture Design (UFD), partitioning the well length and employing a large number of fractures. Design of each fracture is treated separately with an allocated drainage area allowing different aspects ratios in each iteration of design.The UFD approach is augmented by a net present value (NPV) calculation allowing for the critical economic optimization. In past work NPV has been a decisive element in the optimization process, because it utilizes operational costs and hydrocarbon production to evaluate reservoirs which are candidates for exploitation strategies. The number of fractures per well, their spacing and the size of the fractures are the results of this optimization. Actual treatment variables are presented, including all injection variables, fluid and proppant properties.Based on post-treatment well performance, the entire project presented here is marginal when considering economics e.g., the best is a 5-year NPV of $5 million for a horizontal well with four-transverse fractures. A comprehensive approach is required for this reservoir, optimizing well architecture and costs. What we present in this paper is the procedure to achieve the best physical optimization, followed by the proof of economic viability through the NPV calculation.