Integrated Data Analysis and Dynamic Fracture Modeling Key To Understanding Complex Waterfloods: Case Study of the Pierce Field, North Sea

Abstract

The performance of many waterfloods [and enhanced-oil-recovery (EOR) schemes] is characterized by fluid injection under fracturing conditions. Especially when the geology is complex and the mobility of the reservoir is low, induced fractures can be of the same order as the well spacing, which has a significant (in general undesired) impact on both areal sweep and vertical conformance. Therefore, fluid injection needs to be actively managed and surveyed in order to design an appropriate injection strategy over time.We have analyzed historical injection/production-test, injection step-rate-test, and falloff (FO) test (FOT) data of an existing complex waterflood in the Pierce field, North Sea. The mental subsurface model that emerged from this data analysis was developed further through a series of dynamic fracture-propagation simulations. While the data analysis was a relatively standard procedure, the fracture-modeling part was far from trivial and included simulations using a standalone fracture modeling tool and a more sophisticated coupled dynamic fracture-propagation reservoir simulator, both being in-house software tools.The combined analysis was used to develop a better understanding of the waterflood performance. The main improvement compared to previous work was the integration of the data analysis and the dynamic modeling work rather than looking at each data source individually. In combination, a consistent explanation of the observed reservoir behavior was achieved. This has resulted in changes in the day-to-day water injection management and is expected to play a key role in longer-term development strategies Raw-Data AnalysisThe first step toward a better understanding of the Pierce waterflood response was a detailed analysis of all the raw data available such as daily injection/production rates and THP/BHP, step-rate injection test(s), buildup and FOT in producers and injectors, respectively. In the following, we are presenting an example of each of these data groups, while the stress data and pressure-transient data are discussed in separate paragraphs that follow.

Production-Induced Stress Change in and Above a Reservoir Pierced by Two Salt Domes: A Geomechanical Model and Its Applications

“…This triggered an integrated study with the objective of understanding the observations and formulating remedial actions for the short term (water/gas injection optimization) to medium/long term (e.g., infill drilling of producers/injectors). Early results of this study, focusing on the producer-injector pair in the east, have been reported in Hustedt and Snippe (2010). Their model results suggested that tensile (and possibly also shear) fractures grow from the water injector in a direction roughly orthogonal to the salt/sediment interface, i.e., also toward the producer wells.…”

“…1). The pair in the east (A8z-A1) was covered in Hustedt and Snippe (2010). By applying the same methodology (as described in Hustedt and Snippe and summarized in the following) on the other producer/injector pair, we have learned that qualitatively all pairs behave the same in terms of induced fractures.…”

“…The first one is through pressure-transient analysis (PTA) of the fall-off signal during well shut-ins. Details of this method as well as its application on the A8 injector are provided in Hustedt and Snippe (2010). Generally speaking, for each injector there is a reasonably dense set of fall-off data throughout the injection history, because of both planned and unplanned downtime of the injector.…”

Waterflood performance evaluation in a chalk reservoir with an ensemble of tools

“…Many authors reported integrating surveillance data with full-field simulation studies. Some of these studies include those of Hustedt and Snippe (2010), Langaas et al (2007), Bahar et al (2005), and King et al (2002), among others over the last decade.…”

Injection Fall-Off Analysis of Polymer Flooding EOR

“…The method consists of analyzing the pressure transient signal produced when shutting the well. Especially when repeated periodically in the same well, PFO testing provides valuable information on injection performance and in-situ mobility changes, as well as on formation properties, boundaries etc (Hustedt and Snippe 2010).…”