Identification, Problem Characterization, Solution Design and Execution for a Waterflood Conformance Problem in the Ekofisk Field - Norway

Abstract

This paper discusses a field case review of the processes used to identify, characterize, design and execute a solution for a waterflood conformance problem in the Ekofisk Field that developed in late 2012. The Ekofisk Field is a highly-fractured Maastrichtian chalk reservoir located in the Norwegian sector of the North Sea. Large scale water injection in the field began in 1987 and overall the field has responded well to waterflood operations. However, fault reactivation coupled with extensive natural fractures and rock dissolution has resulted in some challenging conformance issues. In late 2014, a solution was executed to control this problem. Details of the diagnostic efforts and how this data was used to identify, characterize and mitigate an injector/producer connection through a void space conduit (VSC) will be outlined and discussed. These diagnostics include pressure transient analysis (PTA), interwell tracers, injection profiles, seismic mapping, fluid rate analysis, fluid composition and temperature monitoring. The importance of this data analysis is the key element necessary to select an effective solution. The selected approach involved pumping a large tapered nitrified cement treatment into the offending injector, which is believed to be the single largest nitrified cement operation ever pumped within the oil industry. Because of extremely rapid communication with an offset producer, a protective gel was used to reduce the risk of cement entry into that producer. A brief review of alternative mitigation options and the reasons for selecting the nitrified cement treatment will be discussed. Additionally, a complete review of the shutoff technique, product, damage mitigation strategy, and complications associated with timing and coordination in an offshore environment will also be discussed. Finally, a summary of lessons learned, job execution observations, post-treatment performance results over the past three years, and forward plans will be presented. Based on these results it is believed that there are a number of opportunities to add strong value through conformance engineering.

Water shutoff and conformance improvement: an introduction

“…Unfortunately, for various reasons (most commonly, financial or manpower-related), adequate characterization of the water production problem often does not occur. To help this situation, many people have offered strategies to attack water production problems (Aamodt et al 2018;Chou et al 1994;Elphick and Seright 1997;Kabir 2001;Love et al 1998;Mennella et al 1999;Pappas et al 1996;Seright et al 2003;Smith et al 2006;Soliman et al 2000;Sydansk and Romero-Zeron 2011) and suggested various categorizations of problems, in an attempt to simplify the analysis. The strategy that we advocate involves looking for and solving the easiest water production problems first.…”

PTA-metrics for time-lapse analysis of well performance

“…Permanent well and reservoir surveillance with PDG and time-lapse PTA is today employed in the oil and gas industry with focus on well performance and behavior with their changes during reservoir life-time, including fluid contact movements and recovery processes (Gringarten et al 2003), (Yaich et al 2012), (Ugoala et al 2013), (Rushatmanto et al 2017), (Suleen et al 2017), (Cassie et al 2018); well stimulations (e.g., acid and fracture jobs) and monitoring of well performance over time (Shchipanov et al 2014), (Shchipanov et al 2017a(Shchipanov et al , 2017b; and any kind of improved/ enhanced oil recovery pilots such as water shut-off (Aamodt et al 2018) and silicate injection (Skrettingland et al 2012), (Skrettingland et al 2014). Figure 1 illustrates typical timelapse pressure transient responses for sequential well shutins from (Shchipanov et al 2017a).…”

“…Further study (Shchipanov et al 2017b) has extended the scope of time-lapse PTA to deal with multiple rate pressure transients and step-rate test analysis to monitor performance of wells with induced fractures. Aamodt et al (2018) discussed water shut-off jobs with massive cement placement into an injection well to improve water conformance control, where permanent pressure surveillance and PTA, including combined flowing/shut-in analysis, were used to identify well communication and to monitor the job efficiency. Recent field study by Walker et al (2021) employed time-lapse PTA to monitor initial phase of production in a giant oil field, where well interference and boundary conditions of the reservoir were disclosed from analysis of time-lapse flowing and shut-in periods.…”