Monitoring of Real-Time Temperature Profiles Across Multizone Reservoirs during Production and Shut in Periods Using Permanent Fiber-Optic Distributed Temperature Systems

Abstract

Abstract This paper describes the use of a fiber-optic distributed temperature system (DTS) to monitor and evaluate the production and shut-in thermal profiles in an offshore China well. The objective was to identify and correlate production changes with respect to time over the first phase of a multi-phase offshore field development. The well was drilled from an offshore platform with a deviation of 40 degree across the reservoir section and completed with a 5 ＿ inch diameter expandable sand screen (ESS). An electrical submersible pump (ESP) was used to produce the oil. The reservoir consists of multi-layered sand zones and the flow was commingled through the sand screens to the pump intake set in a 9–5/8 inch diameter casing. The system was commissioned to acquire a better understanding of the flow allocation in the complex stacked reservoir sequence. The importance of this knowledge in the early stages of production is expected to influence future field development. Continuous distributed temperature monitoring of the well enabled quantitative analysis of the produced fluids to be performed at selected times providing real time, permanent, production monitoring over the reservoir. This technique will allow future wells to be developed with smaller completion sizes by limiting the requirement for production logging "Y" tools. The data acquired to date has provided improved reservoir characterization and understanding of the dynamics of the reservoir behavior. The data analyzed included initial well unloading and clean-up, zone depletion over time resulting from zone reservoir pressure changes, natural flow on shut-in and differential flow induced from various production rates using a variable speed ESP. These key events would not have been captured with conventional production logging due to normal operating constraints. As the completions in this field are multi-zone or multi-layer completions, understanding the relative flow contribution of each zone or layer is important for long-term reservoir management.Combined with pressure transient analysis of initial production history, the data collected from the fiber optic DTS has enabled the determination of individual sand lobe flow capacity and a better determination of net pay cut offs.Combined with other open-hole log information, a breakthrough has been achieved for generating accurate models of permeability for each sand sequence within this fluvial deltaic reservoir environment. Fiber Optic System Installation and Operation The distributed temperature system optical fiber was installed in a ＿ inch diameter 316 control line attached to the 3＿ inch diameter production tubing and supported across the reservoir interval by a 2 3/8 inch EUE stinger hung below the REDA* electrical submersible pump (ESP) and packer assemblies. The production tubing is hung by 4 1/5 inch diameter tubing from a Drill Quip tubing hanger. The fiber was installed in "single ended" format (only one fiber) using encapsulated control line along the reservoir interval for protection and bare control line elsewhere. A twin check-valve and a burst disc assembly were used at the bottom of the control line to provide a dual barrier to the formation. The control line was installed using mid-joint and cross coupling protectors along the stinger (deviated section). The stinger and encapsulated control line are run inside an expandable sand screen (ESS) across the reservoir section, which is 374 meters in length. The well completion diagram is shown in Fig.1.