Well Testing in Tight Gas Reservoir: Today's Challenge and Future's Opportunity

Abstract

With the increase in demand and rapidly diminishing resources in conventional reservoirs, economically producing gas from unconventional reservoirs e.g. tight gas reservoir is a great challenge today. The character and distribution of tight gas reservoirs are not yet well understood. Low quality reservoirs are often seen as involving higher costs and risk than high-medium quality reservoirs. There is no formal definition for "Tight Gas". Law and Curtis (2002) defined low-permeability (tight) reservoirs as those with permeabilities less than 0.1 mD. The best definition of tight gas reservoir is "reservoirs that cannot be produced at economic flow rates or economic volumes of natural gas are unrecoverable, unless the well is stimulated by a large hydraulic fracture treatment or produced by use of a horizontal wellbore or multilateral wellbores." Unlike conventional reservoirs, which are small in volume but easy to develop, unconventional reservoirs are large in volume but difficult to develop. Improved technology and adequate gas price is the key to their development. Gas production from a tight-gas well will be low on a per-well basis compared with gas production from conventional reservoirs. A lot of wells have to be drilled to get most of the gas out of the ground in tight gas reservoirs. Testing a tight gas reservoir is a big challenge today but in coming future more and more numbers of wells are expected in tight gas reservoirs. If we want to grab a piece of this upcoming opportunity, we will have to accept the challenge today. More data and more engineering manpower are required to understand and design a well test in tight gas reservoir than a well test in good permeability conventional reservoirs. In this paper, a possible way to test a tight gas reservoir using hydraulic fracturing will be discussed. Since hydraulic fracturing is one of the most successful ways of producing a tight gas reservoir economically so far, an idea of integrating hydraulic fracturing job with well testing job as a complete package for testing tight gas reservoirs, especially in the exploratory phase, will be discussed.

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