Albena Mateeva

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.

Virtual source applications to imaging and reservoir monitoring

The virtual source method is a breakthrough that allows us to image and monitor the subsurface in cases where surface seismic or VSP fail to deliver. In settings where the overburden is complex or changing, traditional time-lapse signals are weak or nonrepeatable, leading to ineffective seismic input to reservoir modeling and little of value generated by repeated seismic surveys. On the other hand, the virtual source method allows us to image under complex overburden, yields repeatable data for reservoir monitoring, enables shear seismic, and may help us “look ahead” as we drill.

Onshore Monitoring With Virtual Source Seismic In Horizontal Wells: Challenges And Solutions

The Virtual Source (VS) Method provides unparalleled capability to synthesize controlled and repeatable downhole sources at the location of VSP geophones. Although the physical sources are located at the surface, VS redatuming corrects for small non-repeatability of surface shooting and compensates for subsurface changes above the receivers. If Virtual Sources are created at permanently placed receivers, then we essentially obtain a “permanent downhole source and receiver” configuration that is optimal for sensitive reservoir monitoring. We demonstrate these advantages with a field data example and then focus on defining acquisition, drilling and tool requirements for onshore VS monitoring.

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...

Estimating interval shear-wave splitting from multicomponent virtual shear check shots

Measuring shear-wave splitting from vertical seismic profilingVSPdata can benefit fracture and stress characterization as well as seismic processing and interpretation. The classic approach to measuring azimuthal anisotropy at depth involves layer stripping. Its inherent weakness is the need to measure and undo overburden effects before arriving at an anisotropy estimate at depth. That task is challenging when the overburden is complex and varies quickly with depth. Moreover, VSP receivers are rarely present all the way from the surface to the target. That necessitates the use of simplisticassumptionsabouttheuninstrumentedpartoftheoverburdenthatlimitthequalityoftheresult.Weproposeanewtechnique for measuring shear-wave splitting at depth that does notrequireanyknowledgeoftheoverburden.Itisbasedona multicomponent version of the virtual source method in whicheachtwo-component2-CVSPreceiveristurnedinto a2-Cshearsourceandrecordedatdeepergeophones.Theresultingvirtualdatasetisaffectedonlybythepropertiesofthe medium between the receivers. A simple Alford rotation transforms the data set into fast and slow shear virtual check shots from which shear-wave splitting can be measured easilyandaccuratelyunderarbitrarilycomplexoverburden.

Steering Virtual Sources For Salt And Subsalt Imaging

Using walk-away or 3D VSP data to create Virtual Sources in salt is a new useful tool for imaging and assessing drilling hazards in salt and immediately below the base of salt. It can be also used for accurate positioning of steep salt flanks. Creating Virtual Sources inside homogeneous salt allows us to eliminate any distorting effects caused by rugged top salt and complex overburden. The Virtual Source radiation pattern can be controlled and steered in the direction of desired illumination by selecting appropriate shot ranges at the surface. These new Virtual Source applications can have significant business impact for de-risking drilling through salt and improving well targeting in areas with salt.

Estimation of seismic anisotropy from P-wave VSP data

Many rock formations are anisotropic. Their anisotropy, or dependence of seismic velocities on the direction of wave propagation, has been extensively studied and documented throughout the world. It is now widely accepted that understanding subsurface anisotropy yields numerous benefits for both exploration and development of hydrocarbon reservoirs. For example, seismic images produced with ani-sotropic velocity fields are usually crisper and geologically more meaningful than those created with traditional isotropic velocity models. In addition, relating anisotropy to its physical causes (such as lithology, fractures, stresses) enables one to obtain valuable information about them, something that cannot be done if the rocks are deemed isotropic. Making accurate measurements of anisotropy is an obvious prerequisite for all these potential improvements. To be most useful, such measurements should be done in-situ and in the seismic frequency range. Here we discuss a recently developed technique for estimatin...

Accurate Estimation of Subsalt Velocities Using Virtual Checkshots

Virtual Checkshot This paper was prepared for presentation at the 2006 Offshore Technology Conference held in Houston, Texas, U.S.A., 1–4 May 2006. This paper was selected for presentation by an OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Papers presented at OTC are subject to publication review by Sponsor Society Committees of the Offshore Technology Conference. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, OTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435. Abstract

Application of virtual-source technology to the Zuidwending gas storage project

The Gasunie-Nuon Underground Gas Storage Consortium plans to drill and leach caverns in the Zuidwending salt dome in the Netherlands. According to safety regulations, gas storage caverns must be at least 150 m from the salt flank. The location of the Zuidwending salt flank, however, was not well known; its uncertainty based on surface seismic is some ±200 m (Figure 1). A more precise estimate of the salt-flank location was needed for the project to proceed.

Azimuthal Anisotropy Characterization With Multicomponent Virtual Shear Sources At Rulison Field, Colorado

We apply a new method for birefringence analysis at depth to a tight gas reservoir in Rulison Field, Colorado. The new method is based on a multicomponent version of the virtual source method in which VSP receivers are turned into virtual shear sources in the zone of interest. This allows accurate detection of even small amounts of azimuthal anisotropy under complex overburden where traditional methods fail. We used the new method to measure shear wave splitting of less than 1% in a reservoir under significantly anisotropic overburden. That was enough to infer fracture orientation, which turned out to be close to the orientation interpreted from FMI logs.