Applications of broadband seismic inversion in the assessment of drilling and completion strategies: A case study from eastern Saudi Arabia

Abstract

3D geomechanical models have seen a rapid increase in usage within the oil and gas industry. This is driven by the industry's focus on unconventional reservoirs and the subsequent need to understand both wellbore instability during drilling and the drivers for hydraulic fracturing efficiency. Geomechanical models can assist in addressing these questions. In this paper, we demonstrate how broadband AVA inversion models are employed to characterize the Earth's mechanical properties. We then compare stresses computed from our broadband AVA model with those of a computed model utilizing only well log interpolated values. Finally, we show that the employed property model in geomechanical calculations has a significant impact on wellbore stability calculations and fracture propagation pressures. We argue that the use of elastic properties calculated from AVA inversion results in a 3D geocellular model hold significant advantages over the use of properties inferred from well-log interpolation. In addition, the greater fidelity of the elastic properties estimated from broadband seismic AVA inversion has a positive impact on the final geomechanical model. Geomechanical property population from broadband 3D seismic AVA inversionWhen employing 3D geomechanical models, one of the tasks is to build a model of properties representing the elastic response (both dynamic and static) and strength of rock contained in each cell of a geocellular model. Figure 1 shows a gridded model with x and y dimensions of 150m and a variable cell height with average thickness in reservoir layers of 15m. The majority of the model was populated by acoustic impedance (AI) derived from AVA inversion of recently acquired full azimuth broadband data; these data were depth-converted and resampled to the geomechanical modelling grid. Model cells representing the shallow overburden were filled with acoustic impedance interpolated from well logs, while the deep section depth trends, acoustic impedance was calculated from bulk density and stacking velocity trends. In a similar manner, a gridded model of Vp/Vs ratio is created using pre-stack AVA inversion. Using a series of transformsthat relate the models of acoustic impedance and Vp/Vs ratio to static elastic properties (Young's modulus and Poisson's ratio), as well as strength properties (unconfined compressive strength, friction angle and tensile strength) -the geocellular mechanical property models were generated.The quality of our geomechanical model will thus be directly related to the accuracy of estimation of elastic parameters from the seismic volume. One of the most difficult tasks in any AVA inversion process is to obtain a Vp/Vs vs. AI relationship that is compatible with similar log-derived values. Using as an initial source a seismic volume with a broader frequency spectrum rich in low frequency content, as compared with conventional bandwidth land data Giroldi, 2013, Wallick et al, 2012), produces results with greater fidelity to true reservoir properties. This can be seen in Figure 2, wh...

Lithological Characterization by Simultaneous Seismic Inversion in Algerian South Eastern Field

“…In this section, we will begin the application of seismic inversion on real seismic data. The study was carried out on the seismic data of the field situated in the southeast of Algeria, which contains four (4) cubes with four (4) different stack angles: 5-10°, 10-20°, 20-30°, and 30-40° as shown in Figure 1 [3,9]. Four wells (W1, W2, W3, and W4) were drilled in the field as shown in Figure 2, where all necessary logging data (acoustic impedance (AI), Vp/Vs velocity ratio, and density (Rhob)) are available.…”

“…Based on the geological description of the region, core description, and drilling reports eight seismic horizons were confirmed: 1) Maastrichtian, 2) Campanian, 3) Santonian, 4) Coniacien, 5) Turonian, 6) Cenomanian, 7) Albian, and 8) Aptian (Figure 3). Detailed workflow of seismic inversion before summation, applied to the studied field, is given in Figure 4 [5,6,9].…”

3D Geomechanical Model Construction for Wellbore Stability Analysis in Algerian Southeastern Petroleum Field

“…The second part of the paper is dedicated to the construction of the 3D geomechanical model. In order to drill new wells and establish their ideal directions to assure the most effective exploration plan, wellbore stability was also analyzed in this study [11]. By minimizing drilling events and minimizing reservoir damage through an ideal density for drilling mud, a model was considered for optimization of drilling expenses [12].…”