The Value of Surveillance and Advanced Logging Applications for Brownfield Optimization

Abstract

There has been a tremendous growth in the number of high-angle and horizontal wells in the past decade. Coupled with the increase in water cut from various brownfield environments, these high angle wells present us with complex reservoir and production management challenges. Fit for purpose production logging technology is helping to provide a better understanding of fluid movement, enabling higher confidence decision making leading to successful interventions. Production logging in high angle and horizontal wells that produce mixtures of fluid phases is challenging because of the associated complex flow regimes that radically change the physics and technology of measurement. Depending on the borehole deviation, the velocity and fluid holdup of different phases can change dramatically for a given flow rate. We present examples that encompass various reservoir management objectives, well optimization and flow profiling. Surveillance logs were acquired in these wells to obtain key inputs for production optimisation, identifying bypassed oil and evaluating potential for additional perforations. Where necessary, production logs were integrated with pulsed neutron capture and spectroscopy measurements to enhance our understanding. In one of the examples, a compact integrated production logging tool comprising an array of spinners and holdup probes was conveyed with tractor in a horizontal well. Besides conveyance in this horizontal well, the challenge involved detecting minor oil entries in a very high water cut scenario. Two examples relate to the effective use of pulsed neutron spectroscopy measurements reservoirs. Finally one of the examples involves oxygen activation for positive identification of water movement behind pipe. Creating value through surveillance is the common thread that binds these well intervention examples together. Introduction North Sea oil and gas production from mature basins face some particular challenges against a backdrop of production from platform and subsea wells in a challenging offshore environment. These offshore field developments often consist of long horizontal wells with subsea completions, resulting in a high cost of well interventions and technical challenges in the conveyance of logging tools. The importance of surveillance for field management and further brownfield development cannot be underestimated, even though the ultimate benefits are not always apparent in advance. These benefits include, for example, optimizing production, reducing watercut, improving well performance, optimizing water injection and sweep efficiency, and identifying unswept areas of the field to target with further infill drilling activities. In this paper, we present four examples of reservoir surveillance activities in different mature North Sea reservoirs. Each example was selected for illustrating the application of a particular surveillance technology to meet a specific objective. Applying the appropriate measurement tools and techniques is essential to the success of the well intervention. Further, in some cases the results can be surprising and lead to unexpected benefits, as will be described in one of the following examples. Fluid flow regimes in vertical, deviated and horizontal wells In a system with multiphase flow, buoyancy causes the fluids to separate into different phases with a mixing layer in between. Gravity ensures that the lighter phase travels at a faster speed than the heavier phase. The difference in velocity between the phases is referred to as slip velocity. This also causes the downhole holdups to be different from the surface cuts.

Integrated Surveillance Enhancing Quality of Decisions and Reservoir Description in the Harding Field

“…The results of the array PL were interesting and provide new information to understand the recovery of oil in the PS1 well and from the reservoir (Akiode et al 2007). …”