Peter Wills

Distributed acoustic sensing for reservoir monitoring with vertical seismic profiling

Distributed Acoustic Sensing is a novel technology for seismic data acquisition, particularly suitable for Vertical Seismic Profiling. It is a break-through for low-cost, on-demand, seismic monitoring of reservoirs, both onshore and offshore. In this article we explain how Distributed Acoustic Sensing works and demonstrate its usability for typical Vertical Seismic Profiling applications such as checkshots, imaging, and time-lapse monitoring. We show numerous data examples, and discuss Distributed Acoustic Sensing as an enabler of seismic monitoring with 3D Vertical Seismic Profiling. Key words: Borehole geophysics, Acquisition, Seismics, Time lapse, Monitoring.

Monitoring primary depletion reservoirs using amplitudes and time shifts from high-repeat seismic surveys

In the high-porosity, poorly consolidated turbidites of the deepwater Gulf of Mexico, production-induced compaction is the main production-drive mechanism when aquifer support is weak and prior to pressure support by secondary recovery water injection. Time-lapse (4D) seismic monitoring of this class of reservoirs has provided several new learning opportunities. The time-lapse amplitude response of these fields can be complicated due to saturation changes (water replacing oil) inside the reservoir, rock compaction causing density and velocity changes inside the reservoir, stress relief and associated deformation of the rock outside the reservoir, and changes in reservoir fluid pressures due to pore-pressure decrease. Methods that rely on time-lapse amplitude changes with offset to discriminate pressure and saturation changes can help separate and thus simplify the interpretation of some of these effects (Tura and Lumley, 1999; Landro, 2001).

Dual-well 3D vertical seismic profile enabled by distributed acoustic sensing in deepwater Gulf of Mexico

AbstractWe have acquired and processed 3D vertical seismic profile (VSP) data recorded simultaneously in two wells using distributed acoustic sensing (DAS) during the acquisition of the 2012 Mars 4D ocean-bottom seismic survey in the deepwater Gulf of Mexico. The objectives of the project were to assess the quality of DAS data recorded in fiber-optic cables from the surface to the total depth, to demonstrate the efficacy of the DAS VSP technology in a deepwater environment, to derisk the use of the technology for future water injection or production monitoring without intervention, and to exploit the velocity information that 3D VSP data provide for evaluating and updating the velocity model. We evaluated the advantages of DAS VSP to reduce costs and intrusiveness, and we determined that high-quality images can be obtained from relatively noisy raw 3D DAS VSP data, as evidenced by the well 1 image, probably the best 3D VSP image we have ever seen. Our results also revealed that the direct arrival travelti...

Toward affordable permanent seismic reservoir monitoring using the sparse OBC concept

In recent years time-lapse seismic has become a widely established reservoir monitoring technique. This is especially so in the offshore environment where the vast majority of all 4D seismic has been acquired using streamer technology. While there have undoubtedly been significant successes, especially in the North Sea, there is a continuous drive to further improve 4D signal detectability, operational flexibility, and efficient diagnostic generation for decision taking in reservoir management.

Permanent Seismic Reservoir Monitoring for Real-time Surveillance of Thermal EOR at Peace River

Permanent seismic reservoir monitoring (PSRM) solutions, if of high enough sensitivity and low enough cost, can be used to tackle the many known problems faced by seismic monitoring onshore and thereby increase the profitability of such developments. Here we focus on thermal EOR monitoring using continuous seismic, as provided by SeisMovie®, a registered trademark of CGG. We review the PSRM staircase that Shell has climbed since 2009, introduce the most areally extensive deployment at Peace River in Alberta, Canada, and discuss some of the initial findings and plans ahead. We show progress with PSRM to generate better onshore data that will lead to higher recovery, higher production, and safer and cleaner operations. Significant steps were made towards on-demand, lower footprint PSRM, and next steps are set towards cheaper, non-intrusive automated systems that are required for broad application.

Permanent seismic reservoir monitoring using the sparse OBC concept

Summary The sparse ocean bottom cable (OBC) technique is based on acquisition of low fold, but highly repeatable data, resulting in relatively small data volumes. Short acquisition and processing turn-around times enable cost-efficient and rapid 4D decision taking. Permanent seismic reservoir monitoring systems using ocean bottom cables are expensive to install. The sparse OBC concept minimizes the number of receiver cables deployed, and is therefore an attractive proposition as installation costs are much reduced. The design of a sparse survey is based on maximizing 4D repeatability, and aims at imaging 4D changes in the reservoir. A minimal “sparsity” of a survey is required for a basic level of noise suppression and imaging. A dedicated 4D demultiple tool complements the sparse technology. A real data example demonstrates the effectiveness of sparse 4D imaging. The results compare well with those of high multiplicity 4D datasets. A certain ability for noise suppression is lost, however, and a trade-off with low costs, efficiency and short turn-around times is required.

Recent Advances in Seismic Monitoring of Thermal EOR

Well-planned and executed reservoir surveillance has proven to add significantly to the production and ultimate recovery of hydrocarbons, notably in areas of Improved and Enhanced Oil Recovery (IOR/EOR). Recent technological advances in the area of data acquisition and integration have led to increased use of well and reservoir surveillance data to optimize such processes. In the case of thermal EOR, one of the most important subsurface uncertainties impacting performance is heat and steam front conformance, both vertically and arealy. This paper illustrates new geophysical technologies used for monitoring various thermal EOR recovery strategies in The Netherlands, Canada, and Oman. We focus on permanently buried seismic sources and receivers, refraction seismic, down-hole seismic, and the newly developed Distributed Acoustic Sensing (DAS) to enable low-cost and non-intrusive seismic surveillance. These technologies are not without challenges, but our field trials indicate they have the potential to broaden the successful application of reservoir monitoring onshore.

3C Deghosting for Refraction Time-lapse Monitoring

Refraction time-lapse monitoring provides affordable areal measurements of reservoir changes using waves that travel from sources along a fast layer underlying the reservoir. When the waves exit the fast layer, they travel through the reservoir and propagate to the receivers, with corresponding arrival times depending on the state of the reservoir. For thermal EOR, changes in the reservoir can be observed and interpreted from changes in these arrival times. Buried receivers benefit onshore seismic acquisition, partly because statics problems are less severe and because some decoupling from surface waves can be expected. Unfortunately, the statics problem is often just replaced by another problem – surface ghosting with strong near-surface effects. For refraction data, which is lower fold, ghost removal can be even more important than for conventional seismic data. At Peace River in Alberta, Canada, deghosting was carried out using a 3C wave field separation technique used in earlier publications by one of us (De Meersman) to analyse near surface attenuation of shear waves. We demonstrate that the method significantly improves the time shift measurements and demonstrate its use in a processing workflow resulting in an interpretable areal time-shift map for a new refraction time-lapse data set recorded in 2010/2011

Use of time-lapse OBC for post-production shallow monitoring

Summary This paper will highlight the benefit of analysing shallow time-lapse OBC data to monitor changes in the near surface brought about by production activities. Analysis of shallow, horizontally propagating wave modes highlights geomechanical changes at the seabed related to production over short time periods, as well as small-scale changes that warrant evaluation as part of regular field surveillance. Timelapse analysis of these effects can play an important role in deriving technical solutions to protect the long-term value of operations to extend field life. OBC systems are uniquely suited to this analysis.

Monitoring Primary-Depletion Reservoirs With Seismic Amplitudes and Time Shifts

In the high-porosity, poorly consolidated turbidites of the deepwater Gulf of Mexico (GOM), production-induced compaction can be the drive mechanism when aquifer support is weak and before pressure support by secondary-recovery water injection begins. Time-lapse (4D) seismic-monitoring time shifts occur in areas of depletion and in the overburden, and they indicate compartmentalization in the reservoir. Compartmentalization information can help place new production and injection wells better, as well as new sidetracks for optimized field development.