Search

When the drainage area of a flowing well is long and narrow, the pressure transient behavior of the well often cannot be analyzed by conventional means. Well tests which appear to exhibit linear flow behavior for extended periods, beyond the length of time which could be attributed to flow to a fracture, have been observed for both geothermal wells and for oil and gas wells. In geothermal formations and in some of the deep low-permeability gas fields the elongated reservoir shape results from long parallel faults which appear to bound the formations. Typically such wells are also penetrating natural fractures. In other reservoirs the elongated drainage shape is due to the river delta or alluvial environment in which the reservoir sands were originally deposited. Using a recently developed scheme for custom type curve generation for a wide variety of flow geometries, the particular behavior of the well producing from an elongated linear flow system is presented in detail. Cases examined include fractured wells of variable fracture length in varions positions within the flow channel and also of variable length. The effects of partial penetration are also demonstrated. This paper illustrates the use of custom type curves in computer-aided type-curve matching. With the help of relatively inexpensive computer graphics, custom type curves are displayed which exactly represent whatever is known about a particular drainage geometry, including such variables as formation thickness and areal extent, fracture length, partial penetration, and well location. Familles of curves can be generated and displayed along with the data to help determine unknown features of the reservoir geometry. An important contribution included in this work was the development of a set of orthogonal dimensionless parameters which facilitate the generation of familles of type curves which vary one reservoir shape parameter with implied effects on other parameters. The dimensionless solutions for any reservoir geometry are then readily developed for use in computer-aided type curve matching. Lorsque la zone de drainage d'un puits de production est longue et étroite, les méthodes classiques d'analyse du comportement des changements de pression ne peuvent être utilisées. De tels comportements, se prolongeant après la période pouvant être attribuée à une fracture, ont été observés pour des puits produisant de l'huile, du gaz et même pour certains puits géothermiques. La géométrie allongée, que l'on rencontre parfois dans certaines formations géothermiques et poches de gaz à grande profondeur et de faible perméabilité, peut être expliquée par des réseaux de fractures parallèles qui limitent la formation. Naturellement, les puits forés dans de telles formations peuvent traverser des fractures naturelles. Pour d'autres réservoirs, la forme allongée peut être causée par la géométrie de l'environnement dépositionnel deltaïque. Utilisant une méthode récemment développée permettant de produire des courbes caractéristiques de changement de pression pour une grande variété de géométries, le comportement particulier des puits drainant des formations allongées est présenté en détail. Les cas suivants ont été analysés : fissuration avec modification de la longueur de la fracture et diverses positions du puits dans la formation avec pénétration partielle de différentes longueurs. Les courbes sont construites directement sur le terminal. Elles prennent en compte exactement ce qui est connu de la géométrie du réservoir, de l'épaisseur, la forme, la longueur de la fissure, de la longueur de la zone perforée et de la position du puits. Des familles de courbes peuvent être générées et affichées, puis comparées aux données pour déterminer les paramètres inconnus de la géométrie du réservoir. Une contribution importante, présentée dans cet article, est le développement d'un système de paramètres orthogonaux sans dimensions qui facilite la génération des courbes caractéristiques. Les courbes caractéristiques de pression, correspondant à des géométries spécifiques à l'utilisateur, peuvent être superposées aux données de pressions en vue de déterminer les paramètres inconnus du réservoir (type curve matching).

Summary Liquefied natural gas (LNG) has yet to be deployed in the development of offshore fields in spite of several detailed studies completed and offshore technology development demonstrating its technical feasibility. The perceived risks associated with deploying unproven technology in a high construction cost and volatrile gas price environment have so far inhibited offshore liquefaction projects. The potential deployment of such technologies is of paramount importance considering the massive volumes of natural gas currently deemed as "stranded" and the exploitation of which is compelling not only because of the inherent economic benefit but also because of the otherwise adverse impact on oil production. It is conceivable that deep water offshore locations may contain quantities of natural gas rivalling those of onshore locations. Such a statement cannot even be confirmed because drilling for offshore natural gas reservoirs, expected to be found considerably deeper than oil reservoirs, has been unattractive exactly because of the absence of coherent exploitation strategies. If anything, the mere presence of large natural gas deposits even in the form of solution gas in oil is now often considered as largely undesirable because of the cost of just handling non-monetized natural gas. This paper discusses potential offshore LNG processes and reviews natural gas liquefaction cycles in the context of compactness, ease of operation, process safety, and efficiency. Particular attention is paid to the lower-efficiency turboexpander processes for plant capacities up to 3 million tonnes per annum (MTPA, approximately 0.43 Bcf/d). These cycles offer several advantages over the alternative optimized cascade and mixed refrigerant (MR) liquefiers for offshore applications.