Pressure-Transient Tests and Flow Regimes in Fractured Reservoirs

Abstract

Fractures are common features in many well-known reservoirs. Naturally fractured reservoirs include fractured igneous, metamorphic, and sedimentary rocks (matrix). Faults in many naturally fractured carbonate reservoirs often have high-permeability zones, and are connected to numerous fractures that have varying conductivities. Furthermore, in many naturally fractured reservoirs, faults and fractures can be discrete (rather than connected-network dual-porosity systems).In this paper, we investigate the pressure-transient behavior of continuously and discretely naturally fractured reservoirs with semianalytical solutions. These fractured reservoirs can contain periodically or arbitrarily distributed finite-and/or infinite-conductivity fractures with different lengths and orientations. Unlike the single-derivative shape of the Warren and Root (1963) model, fractured reservoirs exhibit diverse pressure behaviors as well as more than 10 flow regimes. There are seven important factors that dominate the pressure-transient test as well as flow-regime behaviors of fractured reservoirs: (1) fractures intersect the wellbore parallel to its axis, with a dipping angle of 90 (vertical fractures), including hydraulic fractures; (2) fractures intersect the wellbore with dipping angles from 0 to less than 90 ; (3) fractures are in the vicinity of the wellbore; (4) fractures have extremely high or low fracture and fault conductivities; (5) fractures have various sizes and distributions; (6) fractures have high and low matrix block permeabilities; and (7) fractures are damaged (skin zone) as a result of drilling and completion operations and fluids. All flow regimes associated with these factors are shown for a number of continuously and discretely fractured reservoirs with different well and fracture configurations. For a few cases, these flow regimes were compared with those from the field data. We performed history matching of the pressure-transient data generated from our discretely and continuously fractured reservoir models with the Warren and Root (1963) dual-porosity-type models, and it is shown that they yield incorrect reservoir parameters.

A Numerical Model for Pressure Analysis of a Well in Unconventional Fractured Reservoirs

“…These effects were investigated using numerical pressure transient testing in this section. Kuchuk and Biryukov [50] applied the semianalytical method to reveal and emphasize its critical effects by analyzing derivative plots. Therefore, the Bourdet derivative plots of the bottom-hole pressure were presented, and velocity and pressure profiles were used to explain the effects.…”

Pressure Transient Analysis and Transient Inflow Performance Relationship of Multiple-Fractured Horizontal Wells in Naturally Fractured Reservoirs by a Trilinear Flow Model

“…Moreover, there have been numerous works analyzing the performance of fractured wells through the transient pressure behavior and production decline analysis. − Zhang et al developed a semianalytical model to investigate the transient behavior of multiwing fractured vertical wells in coal-bed methane gas reservoirs considering the effects of adsorption–desorption, diffusion, and viscosity flow. Wang et al and Kou et al provided novel mathematical models of vertical wells with multiple radial hydraulic fractures in the stress-sensitive coal-bed methane reservoir to simulate the transient pressure responses.…”

Effects of discrete dynamic-conductivity fractures on the transient pressure of a vertical well in a closed rectangular reservoir

“…Unlike hydraulic fractures that connect to the wellbore, discrete fractures and faults may not be connected to the wellbore but, rather, are at a distance. The effects of discrete fractures on pressure responses have also been studied 20 – 27 . Givens and Crawford 20 studied the influence of isolated fractures on fluid-displacement response.…”

“…Based on their work, three flow regions, i.e., fluid flow near the wellbore, fracture-dominated fluid flow and fluid flow in the matrix away from the fracture can be identified. Biryukov and Kuchuk 26 , 27 presented a mesh-free semi-analytical solution for pressure-transient behaviour in a 2 Dimensional infinite reservoir containing a network of discrete or connected finite- and infinite-conductivity fractures.…”

“…As noted above, the transient pressure behaviours of wells due to constant-conductivity fractures 6 – 19 and dynamic-conductivity fractures have been discussed 28 – 33 . In addition, transient pressure responses of wells near constant-conductivity fractures have been studied 20 – 27 . However, to the best of our knowledge, few studies have discussed the transient pressure behaviours of wells near discrete fractures with dynamic conductivities in closed rectangular reservoirs.…”