4D Seismic Application In Reservoir Characterization And Residual Oil Distribution Prediction Of AAA Oil Field

Time-lapse seismic can be an important tool for monitoring and planning further development of a producing hydrocarbon field. Using of4D seismic make it possible to detect production changes over a relatively large area and match these changes with production data acquired from wells. Undepleted/unflooded patches, pressure barriers and injectors out of range can be revealed when interpreting a4D data set. This can be valuable information when updating reservoir models and planning new wells, and eventually will lead to an increased recovery from the field.This thesis focuses on the methodologies of4D application in reservoir characterization and residual oil distribution prediction. To get explicit explanation of the methodologies this study work on, this thesis try to answer five questions as follows:(1)What is4D technology, its history and its future holds?(2)Which types of reservoirs are suitable for4D implementation?(3)What is the rock physical basis of4D seismic application in reservoir characterization and residual oil distribution prediction?(4)What are the theoretical and empirical methodologies of4D application in reservoir characterization and residual oil distribution prediction?(5)How to use and what is the workflow of these methodologies in practical case?The answer for the first question is comprised of four parts. The first part gives a definition for4D seismic technology and its value which includes:●Improve geological model of reservoir●Monitor dynamic changes of producing reservoir●Adjustment to the development plan●HSSE monitoringThe second part is a summarization of the brief history of4D technology which includes three stages: ●Stage1is between1983-1990, which is the emerging of4D seismic technology.●Stage2is between1990-2000, which is the fast growing and developing phase.●Stage3is between2000-present, which is the widely implementation and maturing of4D seismic technology. The third part introduces some4D acquisition and processing techniques. Those acquisition techniques include:●Marine Streamer Acquisition●Ocean Bottom Nodes●Ocean Bottom Cable●Onshore acquisitionMost representative4D acquisition tools from different Geophysical companies are introduced. This thesis also gives a comparison between different4D acquisition techniques. The introduction of processing technique is comprised of general principals of processing, workflow of4D seismic processing and the unique elements of4D seismic processing different from conventional3D seismic processing. The processing workflows of BGP and CGG are illustrated in the thesis. The fast-track and parallel processing workflows of CCG used in AAA oil field are also introduced in this thesis. Four unique4D seismic processing elements are introduced in this thesis which include:●Statics&De-striping●Regularization●4D Binning●MatchingThe fourth part predicts the future of4D technology. This thesis predicts five possible directions related to the future development of4D technology, which are:●More widely used in various oil fields.●Offshore application seeing a brighter future than onshore.●Integrated with other technology to get more information from subsurface.●Permanent, fixed, downhole and seabed survey will be next generation’s tendency.●Precisely and quantitatively measurement of reservoir changes.The second question is about the feasibility of4D seismic. Feasibility studies are key elements of4D seismic and field life-cycle planning. Feasibility study of4D seismic can be further subdivided into two levels, the first level is screening with4D-technical-risk spreadsheet. The essence of the4D-technical-risk spreadsheet is qualitative assessment of the reservoir with key elements which4D seismic has the most sensitive response to them. This thesis illustrates several most recognized4D-technical-risk spreadsheets in4D screening. Alternatively, sophisticated simulation-to-seismic modeling can help us to assess the magnitude and interpretability of the4D seismic response and can help us to plan the optimal timing of repeat surveys. The modeling can be done with well logs or a3D reservoir model. For the most part, industry has used these tools effectively to high-grade the application of4D technology and, in so doing, to minimize the number of technical failures. We generally know whether4D will work in our reservoirs and when to acquire repeat surveys. This thesis also uses AAA oil field as a modeling example of feasibility study. Through the practice of AAA oil field, this thesis gets four conclusions:●4D changes will probably be more obvious on the near offsets than on the far offsets.●We should be able to detect4D signal as small as1.5%AI change.●In a worst case (i.e. noisy acquisition/poor processing) this might increase to2.5%AI change.●On the far-offsets, we should be able to detect a2.5%change (4%in a worst case).To answer the third question, this thesis briefly introduces the fundamental of rock physics and geomechanics which are used to translate production induced changes in the subsurface elastic properties to the seismic responses. We also explain how this is implemented in our modeling. In general, there are four main parameters that may change in a producing hydrocarbon reservoir, they are fluid saturation, pressure, compaction, temperature. This thesis explicitly narrates the rock physical basis of those four fundamental reservoir changes’ relationships with4D seismic responses.About the fourth question, there are two aspects included in it. The first part is4D seismic application in qualitative reservoir characterization. This thesis summarizes some theoretical approaches of using4D seismic attributes in interpretation of reservoir changes. Those attributes include amplitude, time-shift, impedance, AVO and EEI. For qualitative interpretation approach, this thesis also proposes a Colour Index (CI) template combined with geophysics theory and regional experiences to indentify different phenomena came out in the course of production. Those phenomena include:●Compaction●Replacing oil with water●Reducing pore pressure●Replacing HC with water●Replacing gas with oil●Increasing pore pressure●Gas injection●Gas come out of solution●Replacing oil with gas●Gas come out of solutionAnother part of the fourth question is about4D seismic application in prediction of the changes of dynamic reservoir parameters. Many researchers have studied different ways to estimate fluid saturation and pressure changes during production with different4D seismic attributes. Tura and Lumley (1999) present a method to map and quantify those changes utilizing P-and S-wave impedances. Rojas (2008) proposes to use the P-and S-wave velocities ratio as an indicator of lithologies, fluid saturation, and pressure changes in gas sandstones reservoirs. Landra (2001,1999) introduces an elegant, straightforward inversion scheme that solves for pressure and saturation changes from seismic amplitude-variation-with-offset, etc. This thesis proposes a new methodology which uses time-lapse extended elastic impedance (EEI) for estimation of fluid saturation and pressure changes. Extended elastic impedance is introduced by Whitcombe et al. in2002for the first time. It is used as a replacement of El (elastic impedance) in reservoir and hydrocarbon prediction at the exploration phase. Since it improves the stability of elastic impedance, it is good for a more accuracy quantitative estimation of fluid saturation and pressure changes. So from theoretical side, EEI has the natural advantage to become the right attribute adapt to quantitative4D interpretation. EEI has been used for almost ten years, but rare previous applications in4D monitoring cases were found. This thesis uses the regression equations and extended elastic impedance inversion to estimate the lateral changes of fluid saturation and reservoir pressure get a very good effect. This thesis also summarizes the workflow of using time-lapse EEI in estimation of fluid saturation and pressure changes as following steps:Step1:Compute EEIx logs with exist wireline logs.Step2:Cross-plot Sw, Sg with EEI at different theoretical angers and define the best correlation anger. After this work, we can get the best correlation theoretical anger X-Step3:Regressional analysis and get the quadratic equations between△Sw,△Sg,△P and△EEIX.Step4:Implement the EEI inversion and get AEEIx cube.Step5:Use the regression equation between△Sw, ASg,△P and△EEIχ t0compute the△Sw,△Sg,△P values with the inversion AEEIχ cube.About the fifth question, this thesis uses AAA oil field as a practical example, illustrates the workflow of using4D seismic data in reservoir characterization and residual oil prediction. This thesis proposes an iterative methodology based on advanced history matching solutions to constrain3D stochastic reservoir models to both production history and4D seismic attributes. In this approach, geostatistical modeling, upscaling, fluid flow simulation, downscaling and petro-elastic modeling are integrated into the same history matching workflow. Simulated production history and4D seismic attributes are compared to realizations, and finally decide the last version of geological model. This thesis not only explains the theoretical basis but also use AAA oil field as an example illustrates the4D seismic application in as follows:●Structural model modification (localised fault, well positioning errors highlighted by4D).●Compartmentalization (includes faults transmissibility and permeability porosity trend).●OWC, GOC or addition portion of hydrocarbon to the edge of the grid.●The seismic architectural elements and facies association (control the trend of sand distribution, specifically using the simulated output data to match with the4D anomalies with iterative process to get the best correlation).●The addition of baffles or barriers (particularly those suggested by pressure transient analysis or the4D seismic).●The addition of connectivity of different sandbody (particularly those suggested by the4D seismic).