Automated Approach Optimizes Flow-Control Device Placement in SAGD Completions

Abstract

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 193364, “Optimization of Placement of Flow-Control Devices Under Geological Uncertainty in Steam-Assisted Gravity Drainage,” by Siavash Nejadi, Stephen M. Hubbard, Roman J. Shor, SPE, Ian D. Gates, SPE, and Jingyi Wang, SPE, University of Calgary, prepared for the 2018 SPE Thermal Well Integrity and Design Symposium, Banff, Alberta, Canada, 27–29 November. The paper has not been peer reviewed. Steam-chamber conformance in steam-assisted gravity drainage (SAGD) influences the efficiency and economic performance of bitumen recovery. Conventional SAGD well-completion designs provide limited control points in long horizontal well pairs, leading to development of nonideal steam chambers. The complete paper presents an automated approach to optimizing placement of flow-control devices (FCDs) in SAGD well-pair completions. The methodology uses a coupled wellbore/reservoir model to simulate both reservoir fluid-flow behavior and detailed wellbore hydraulics. The qualities of the well-completion-design parameters and their effect on production are assessed by calculating the net present value (NPV), which is considered the basis for•optimization. Introduction The Lower Cretaceous McMurray formation hosts the majority of bitumen in the Athabasca oils sands—the largest known resource of bitumen. The formation is composed of large-scale fluvial-estuarine point bars and other laterally accreting channel systems that are highly heterogeneous. The formation has been interpreted as having three stratigraphic subdivisions: a lower continental (fluvial), a middle fluvial-estuarine unit (point-bar dominated), and an upper marginal marine deposit. The repeated erosional cut and fill events within the McMurray have led to nested and multiple stacked structures. Similarly, laterally accreting channel systems, such as point-bar deposits consisting of inclined heterolithic strata of sandwiched sand-siltstone sequences and abandoned mud channels, lead to very complex sedimentary facies relationships in which rock types change both laterally and vertically over very short distances. SAGD completions offer the most promise of producing bitumen resources from Athabasca oil-sands deposits. The SAGD well configuration typically consists of two parallel horizontal wells within a short distance, one above the other. Steam is injected into the upper well and fluids are produced from the lower well. These design schemes provide limited control of steam injection and liquid production along horizontal sections and adversely affect steam-chamber conformance. Operational difficulties, drilling, well completion, and reservoir parameters moderate overall SAGD performance. More specifically, these factors include hydraulic gradients and pressure drop in the tubulars, injectivity and productivity variations along the wellbore from plugging and formation damage, heat exchange, energy loss to bottom water, nonparallel well-pair placement, well undulation, and—most importantly—reservoir heterogeneity and structure. The conventional SAGD well completion needs to be modified to deliver steam efficiently throughout the reservoir interval, improve liquid-production performance, and minimize steam breakthrough.