Analysis of Production Data from Fractured Shale Gas Wells

Abstract

Long-term shale gas well performance characteristics are generally not well understood. The ultra-low permeability of shale ensures the continuing presence of pressure transient effects during well production. This makes production forecasting a difficult and non-unique exercise. Conventional methods have proven to be too pessimistic, in many cases, because they assume a depletion-dominated system. Recently, more suitable forecasting methods have been developed that account for long-term transient effects. These methods incorporate a transient model (usually linear flow) which transitions into a conventional boundary-dominated flow model after a prescribed time or upon achieving a certain region of investigation. The underlying concept assumes that once a transition to boundary-dominated flow is observed, depletion will dominate the production going forward. Although this methodology has been successfully applied for a variety of tight gas reservoirs, it may not be the right model for fractured shale gas (and some conventional tight gas) reservoirs. Fractured shale gas reservoirs get their productivity from the stimulated reservoir volume (SRV), which may be quite limited in areal extent but is surrounded by a low-permeability reservoir (matrix). Thus, the mechanism for long-term production includes a late-time transition from depletion of the SRV, back to infinite acting (linear or pseudo-radial) flow. This "return" to infinite acting flow may or may not provide contribution to recoverable reserves within a practical time-frame, but it should be considered nonetheless. In this paper we present a straight forward methodology for determining the major well performance characteristics of fractured horizontal shale gas wells, considering the impact of uncertainty and non-uniqueness. The focus will be on determining the dominant flow regimes and bulk properties from the data, and then defining a suitable, simple reservoir model for production forecasting, using practical experience and all available information. Field examples from the Barnett, Marcellus, and Haynesville shales are included.

Unconventional gas reservoir evaluation: What do we have to consider?

“…Whenever possible, production analysis should be combined with other surveillance data such as microseismic, production and tracer logs, so that flow regimes encountered during the analysis can be interpreted for physical meaning. In the tight gas example that follows, we discuss integration of data for a more meaningful analysis e for shale gas reservoir examples, we refer to Anderson et al (2010).…”

Wpływ niepewności wybranych parametrów geologicznych i błędów pomiarowych na wyznaczanie wydobywalnych zasobów gazu w krajowych formacjach łupkowych metodą krzywych spadku wydajności

“…Zastosowano metodykę przedstawioną w artykułach [13,14], polegającą na wykorzystaniu symulacyjnych modeli złożowych [1,4,5,8,11] o parametrach geologicznych i charakterystykach udostępnień typowych dla dotychczas nawierconych i testowanych krajowych formacji łupko-wych [9]. Ze względu na ograniczony zestaw takich danych oraz z powodu potrzeby analizowania dużego zbioru alternatywnych wariantów analizę przeprowadzono dla stosunkowo szerokiego zakresu słabo rozpoznanych parametrów formacji oraz dla ściślej zdefiniowanych parametrów, które zostały precyzyjniej określone.…”

The RealGas and RealGasH2O options of the TOUGH+ code for the simulation of coupled fluid and heat flow in tight/shale gas systems

“…Prior to the development of models for multiply-fractured horizontal wells (Medeiros et al, 2006), it was common practice to represent these multiple fractures with an equivalent single fracture. More recently, several other analytical and semi-analytical models have been developed (Bello and Wattenbarger, 2008;Mattar, 2008;Anderson et al, 2010), but these, despite their speed, cannot accurately handle the very highly nonlinear aspects of shale-gas and tightgas reservoirs, cannot describe complex domain geometries, and cannot accurately capture gas sorption and desorption from the matrix (a non-linear process that does not lend itself to analytical solutions), multiphase flow, unconsolidation, and several nonideal and complex fracture networks (Houze et al, 2010).…”