We present a unique methodology designed for evaluation and optimization of multi-fractured wells in stacked pay reservoirs using commingled production. The specialized diagnostic procedures are based on rate-transient analyses, and uses historical production data (rates and cumulative) and the results from production logs to; 1) determine the flow rates for each individual stage in a multi-fractured well, 2) apply rate-transient solutions that use rate-normalized-pressures and superposition-in-time to evaluate response accordingly to the fracture flow periods, 3) estimate reservoir and fracture effective properties and 4) evaluate the completion efficiency.
The field examples presented in the paper, demonstrates the application of the production optimization methodology in practice. The approach permits quantification of the reservoir and fracture properties on a layer-by-layer, or frac stage-by-stage, by evaluating the production well history as an extended drawdown and in combination with direct physical measurements of the flow rates and flowing pressures. Such a unique procedure provides a great advantage since parameters such as; permeability (keffective), fracture length (Xf, effective), conductivity (kfbf)effective and dimensionless conductivity (CfD or FCD) can now be obtained for each individual fracture stage. In addition to the effective properties, the methodology allows for estimation of the drainage area and skin for unfractured zones and fracture half-length and conductivity for the hydraulically fractured reservoir layers.
The methodology is applicable to all types of reservoirs, however most of our field experience has taken place in the evaluation and optimization of stacked-pay tight permeability reservoirs and low conductivity fractures where other forms of conventional reservoir characterization techniques are technically difficult and/or cost-prohibitive.
The optimization methodology allows evaluation of the fracture performance efficiency in terms of the reservoir response and contribution, identification of non-fractured zones, bypassed zones (zones without a frac), under-designed fractures, low conductivity values (and steps for improving it), re-fracturing candidates and identification of remaining well potential deliverability.
Introduction
Optimization of the productivity of an oil or gas well is a process of evaluating all of the available practical completion and operating condition scenarios that can be applied to a well to achieve maximum productivity. The objective is to significantly increase the productivity of the well, to maximize the financial performance of multi-fractured wells. From a performance perspective, the optimum production and completion would be the one that results in the maximum economic benefit to the operator.
In practice, the optimum completion design and operating condition well/reservoir production option used will commonly be the optimum solution indicated on an economic basis, or at least a reasonable melding of the optimum economic and technical options considered.
An innovative, robust, and unique production optimization methodology is reported in the paper that permits the quantification of the well and reservoir in situ properties on a layer-by-layer, zone-by-zone, or frac stage-by-stage basis by evaluating the drawdown production performance of the well, in combination with direct physical measurements of layered reservoir flow rates and wellbore flowing pressures.
Methodology
The completion and production optimization methodology reported here, relies on determination of the completion efficiency in terms of the evaluation of the in-situ reservoir and well properties from multilayer reservoirs. This is achieved byCharacterization of hydraulic fractures, individual or within a multi-fractured system (equivalent fracture), by means of the dimensionless fracture conductivity, dimensionless stimulation index and dimensionless productivity solutionAnalysis of the allocated flow rate contribution from each individual completion, by using specialized quantitative rate transient diagnostics and analyses based on the distinctive behavior of transient fracture flow.
