Evaluation of Commingled Reservoir Properties Using Production Logs

Abstract

This paper presents the results of an investigation concerning the development of a reliable and accurate technique for establishing the stabilized deliverability performance of multi-layer commingled systems using multi-rate production log measurements. Both linear and non-linear systems are addressed in this paper, providing a basis for the analysis of reservoirs exhibiting Darcy and non-Darcy flow, respectively. Extension of the conventional Selective Inflow Performance analysis is also presented in this paper to obtain estimates of the formation and well completion properties such as effective permeability, radial flow steady state damage /stimulation skin effect, and non-Darcy flow coefficient. In the specific case where the deliverability performance of a vertically fractured well is considered, estimates of the effective fracture half-length and average fracture conductivity may be derived from the analysis. In cases where the multi-rate deliverability tests are performed under boundary dominated flow conditions, conventional deliverability analysis techniques may also be employed to derive estimates of the reservoir drainage area in addition to the well and reservoir parameters that can be obtained in a transient flow analysis. Applications of the analyses reported in this paper demonstrate the use of the analyses to evaluate the inflow performance measurements of commingled multi-layer reservoirs obtained using multi-rate production logs. Introduction The analysis of the effect of a variable flow rate production history on the pressure transient performance of a well under Darcy flow conditions has conventionally been accomplished using the convolution of the varying flow rate and pressure history of the well to evaluate the transient performance. This relationship is presented in integral form in Eq. 1 and has been utilized for quite a long time1 in the analysis of the transient pressure behavior of oil and gas wells. (1) The dimensionless wellbore pressure at any point in time (tD) is shown to be a direct function of the varying flow rate and pressure history of the well prior to that point in time. The integral relationship given in Eq. 1 can be readily evaluated as a summation of discrete intervals of time for which the flow rate history is assumed to be piece-wise continuous, as a series of constant flow rate steps. This concept is expressed mathematically with Eq. 2 and has commonly been used as the basis for correlating the effects of a variable flow rate history on the pressure transient behavior of a well with the solution for a constant flow rate inner boundary condition. (2) The definitions of the dimensionless variables used in this superposition relationship are given in terms of consistent units for slightly-compressible liquid flow analyses with Eqs. 3 through 5 for time, flow rate, and wellbore pressure, respectively. In the case of an unfractured vertical well, the system characteristic length (Lc) is equal to the wellbore radius (rw).

Evaluation Method of Reservoir Producing Status Based on Cumulative Distribution Curve of Oil Displacement Efficiency

“…Therefore, effective estimation of the reservoir producing status plays a vital role in the accurate evaluation of oilfield development effect. There are many methods for evaluating the reservoir producing status [3]. Based on the specialty, they are divided into geological and seismic methods: reservoir engineering [4], well test [5], numerical simulation methods, indoor experimental techniques, and so on.…”

Characterization of Multilayer Reservoir Properties Using Production Logs

“…25 In a similar manner, Zeng and Zhao 7 also developed separate and specific pressure transient solutions of an unfractured well with non-Darcy flow for a single rate drawdown, pressure buildup following a constant rate drawdown, and even described the technique necessary for extending this type of analysis to multi-rate inner boundary condition transients in general when non-Darcy flow effects must be considered. In addition, both the Spivey et al 6 and the Zeng and Zhao 7 models considered the near-wellbore completion and reservoir non-Darcy flow effects separately.…”