During the past year, our research effort has continued to focus on borehole acoustics and reservoir characterization. The papers presented at the annual meeting, and those included in this volume, include theoretical developments as well as laboratory measurements and field data applications. Our aim is to improve our ability to estimate reservoir properties that impact production

Burns, Daniel R.

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Executive SummaryDaniel R. BurnsEarth Resources LaboratoryDept. of Earth, Atmospheric, and Planetary SciencesMassachusetts Institute of TechnologyCambridge, MA 021391 IntroductionDuring the past year, our research effort has continued to focus on borehole acoustics and reservoir character-ization. The papers presented at the annual meeting, and those included in this volume, include theoreticaldevelopments as well as laboratory measurements and field data applications. Our aim is to improve ourability to estimate reservoir properties that impact production.2 Borehole SeismicsIn the area of borehole seismic applications, five papers are included covering laboratory measurements ofacoustic LWD (Rao et al., 2002), acoustic logging data analysis applications (Briggs et al., 2002; Grandi etal., 2002), and theoretical developments in numerical modeling (Zheng and Huang, 2002; Huang et al., 2002).One of these papers (Grandi et al., 2002) investigates the effect of in-situ stress variations on borehole stabilitythrough the use of finite element modeling of mechanical behavior, as well as field data analysis. Their resultsshow agreement between field data and deformation modeling based on an anisotropic horizontal stress field.This paper takes the first steps towards investigating borehole behavior in a dynamic way through the useof a coupled fluid flow-mechanical modeling approach. We look for more developments in this area throughthe use of a reservoir simulator to calculate stress changes due to production and a deformation model totrack possible borehole instability. The potential for a coupled fluid flow-porous medium deformation modelmay also be investigated.Acoustic Logging-While-Drilling (LWD) applications are becoming more commonplace, especially in deepwater, high-risk wells. The presence of a large diameter, rigid tool in the borehole presents a number ofcomplications to our ability to model and analyze such data. Rao et al. (2002) discuss a laboratory scalemodel experiment of a dipole LWD tool in an anisotropic formation. Flexural modes were excited in boththe fast and slow directions in this experiment. These results show that when tool modes are minimized,the fast and slow shear wave velocities of the formation can be measured. Because the dipole transducerswere not perfectly matched, the compressional arrival was also measured in this experiment.Numerical modeling of the acoustic wavefield in the LWD geometry is somewhat problematic with finitedifference methods because the large diameter tool results in a thin fluid annulus region in the borehole.Huang et al. (2002) address this issue by developing a 2.5-D variable grid finite difference method. Theypresent the formulation of the method, which uses a grid-stretching algorithm, as well as initial tests thatshow excellent agreement with analytical solutions. Zheng and Huang (2002) present an improved absorbingboundary layer approach for both finite difference and finite element modeling that will be beneficial forLWD modeling, as well as other borehole and seismic numerical modeling applications. The method createsa perfectly matched layer (PML) with a reflection coefficient of zero and high attenuation to remove both Pand S waves at any angle of incidence. Initial tests of the method are very promising.Briggs et al. (2002) present an inverse method to rotate cross dipole log data into the slow and fastdirections and find their dispersion curves simultaneously. Initial results on synthetic and field data arepromising.13 Reservoir Characterization and DynamicsIn the area of reservoir characterization six papers were prepared and presented, four of which are includedin this report. Al-Dajani and Tokso¨z (2002) develop an analytic expression for non-hyperbolic reflectionmoveout in orthorhombic media with horizontal interfaces. They also find that the azimuthally-dependentstacking velocity and quartic moveout coefficient can be calculated with good accuracy using Dix-typeaveraging for VTI media, which allows them to extend the non-hyperbolic moveout equation to more generalhorizontally stratified anisotropic media.Kane et al. (2002a) present a joint inverse method for deconvolution and geostatistical interpolationof seismic data, which effectively allows well data to improve deconvolution and seismic data to improveinterpolation of well log data to the interwell region simultaneously. They apply the method to 2-D and3-D field data sets with good results. Al-Moqbel et al. (oral presentation) used the same 3-D data set andidentified seismic attributes (amplitude, phase, frequency, and impedance) that could be used to predict thespatial porosity distribution in a portion of the Ghawar Field in Saudi Arabia. Results were compared tolog data from 21 wells, and to well productivity.Kane et al. (2002b) and Herrmann and de Hoop (2002) introduce fractional spline wavelets to seismicanalysis applications. Kane et al. (2002b) use this family of wavelets as a basis for the inversion of traveltime data for slowness estimation. They show that this wavelet-based method outperforms traditional least-squares methods of solution. Herrmann and de Hoop (2002) develop a matching pursuit technique fortracking variations in seismic reflections (singularities) through a data volume and relating those variationsto geologic transitions. Their method uses multifractional splines to define a dictionary of seismic waveformsparameterized by the localized scale, order, and direction of the singularity. They apply the method toseismic field data and show the value of the approach in both the analysis of interfaces and data de-noising.Finally, Sze and Toksoz (oral presentation) illustrated the use of induced seismicity in a producingreservoir for imaging of subsurface fault planes. They showed that by using a more accurate event locationmethod (double difference relative event location), fault planes could be imaged with improved resolution.This is a developing area for the Lab, and we expected more results involving the monitoring of reservoirdynamics with passive seismic methods.4 Electroseismic and Fluid FlowThe estimation of fluid flow parameters continues to be an important research direction for the Lab. In thisreport we include four papers in this area. Three of these are in the area of seismoelectric/electroseismicmethods, and one involves modeling and visualization of fluid flow in fractured media. Zhu and Tokso¨z(2002) present results from a laboratory study of seismoelectric conversion in fluid-filled fractures in a crosswell geometry. They show that an electrical signal is created when a seismic pulse generated in a boreholeinteracts with an isolated fracture in a reservoir. They also show that this electrical signal can be measuredin a second borehole at some distance from the fracture. This result suggests that it may be feasible touse such a method to detect and characterize permeable structures in the interwell region of a reservoir.Much additional work remains to be done to quantify this effect. Reppert and Morgan (2002) and Reppertet al. (2001) investigate the frequency dependent behavior of the electrokinetic conversion coefficient in acontrolled laboratory setting. They look at both the seismoelectric effect as well as the electroseismic effect.Their results are in good agreement with existing theoretical models, and suggest that it may be possible toestimate permeability from frequency dependent measurements in the field.Sarkar et al. (2002) present results of a numerical modeling study of fluid flow in fractured media. Thevisualization of the flow velocity field in a variety of fracture geometries in 2-D provides insight into theeffect of variations in fracture aperture and geometry on fluid flow. These methods will be extended to 3-Dand used to develop methods for incorporating fractures into reservoir simulators.25 Future DirectionsIn the coming year we will focus our research efforts in the following areas: 1) borehole seismics, 2) electro-seismic methods, 3) reservoir characterization, and 4) reservoir dynamics.In the borehole seismics area we will continue to work on acoustic LWD applications, anisotropy andstress estimation from cross dipole logs, borehole stability modeling, and also move back into some boreholeimaging applications, such as single well imaging, reverse VSP, and seismic-while-drilling.In the area of electroseismic and electrical methods, we will continue our efforts on the basic laboratory ex-periments necessary to develop a method for the estimation of permeability from seismoelectric/electroseismicmeasurements. Electrical imaging methods will also be explored.Reservoir characterization research will focus on fractured reservoirs and methods for incorporating seis-mically derived fracture information into reservoir simulators. We will also continue to investigate reservoirheterogeneity estimation from seismic data in a more general sense.Finally, in the area of reservoir dynamics, we plan to investigate ways of using induced seismicity inproducing reservoirs for subsurface imaging and in-situ stress monitoring. We will also begin efforts oncoupling fluid flow modeling with geomechanical modeling of reservoirs.3

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