Explicit Determination of Reserves for Variable-Bottomhole-Pressure Conditions in Gas Rate-Transient Analysis

Abstract

Summary Current rate-transient-analysis tools for gas wells producing under boundary-dominated-flow (BDF) conditions largely rely on the deployment of the Arps empirical decline models (Arps 1945), or liquid-based analytical models rewritten in terms of pseudofunctions. Recently, Stumpf and Ayala (2016) demonstrated that, contrary to common practice, decline exponents (b) used in Arps’ hyperbolic equations when applied to gas-well analysis can be rigorously estimated before any field-production data are collected. This determination is solely dependent on gas pressure/volume/temperature (PVT) properties and prevailing constant-bottomhole-pressure (BHP) specification for volumetric, single-phase gas-flow conditions. In the study, we extend that work to a more-realistic variable-BHP condition, which is the most common production-specification condition, in terms of the ratio of changing BHP to average reservoir pressure. The decline exponent (b) is thus rederived, and it is shown that under such conditions, variable BHP hyperbolic decline coefficients become solely dependent on fluid PVT properties and take their largest possible magnitude compared with constant-BHP production. Step-by-step analysis procedures are presented that enable explicit and straightforward estimation of original gas in place (OGIP) and other reservoir properties by universal-type-curve and straight-line analysis. Finally, several cases using simulated and field data are discussed in detail to validate the capabilities of the proposed approach.

Dynamic Material Balance Method for Estimating Gas in Place of Abnormally High-Pressure Gas Reservoirs

“…Figure 8 shows the production history for gas well H-58 presented by Ibrahim et al (2003) [40] and Wang and Ayala (2020) [17]. The reservoir and gas properties for the well are listed in Table 14.…”

“…The simulated production data (such as production rate, bottomhole pressure, and cumulative gas production) under various scenarios are derived from Eclipse, a commercial reservoir simulator. The field case is derived from Wang and Ayala (2020) [17] and Ibrahim et al (2003) [40].…”

“…In general, the traditional material balance equation or related methods can be directly used to calculate GIP, whereas well shutdown or well testing to determine the average reservoir pressure results in loss of production and expensive cost. Alternatively, those methods using production data [13][14][15][16][17] almost do not reckon in the characteristic of abnormally pressured gas reservoirs, a fact that the elastic effects of rock pore and irreducible water are often not negligible as the formation pressure decreases [18,19]. Therefore, this paper, taking the pore reduction in reservoir rock and the volume increase in bound water into account, develops an iterative calculation technique for determining gas in place of abnormally pressured gas reservoirs, an improvement of Matter's dynamic material balance, based on a new total compressibility definition and the new material balance equation.…”

Investigation on the pressure response behavior of two-layer vertical mixed boundary reservoir: field cases in Western Sichuan XC gas field, China

“…Appendix A in reference [11] gives the dimensionless mathematical model of Figure 2 in the Laplace domain through the Laplace transform [18][19][20]. Based on the Bessel equation solution [21], Cramer's rule [22], Duhamel's principle [23], and Stehfest numerical inversion [24], Appendix B in reference [11] provides the dimensionless bottom-hole pressure response solution in the real-time domain.…”

The Numerical Simulation Study of the Oil–Water Seepage Behavior Dependent on the Polymer Concentration in Polymer Flooding

“…After the primary depletion and the waterflooding developmental processes, there is still much oil remaining in reservoirs [1][2][3]. Since the water cut of oil blocks gains over 90%, resulting in no longer remarkable waterflooding economic benefits, polymer flooding has been widely applied in oilfields as one of the main enhanced oil recovery (EOR) methods [4][5][6].…”