Summary: Borehole microseismic monitoring is a widely used method in the oil and gas industry to monitor hydraulic fracturing operations. Sometimes, the quality of acquired microseismic data is relatively poor due to lack of proper survey design. The authors provide a comprehensive and thorough workflow, using multiple criteria decision analysis (MCDA), to optimize microseismic acquisition design. The result of this work is a software application, that will help the user determine optimized locations for placing receivers in observation wellbores. Introduction: Development of unconventional reservoirs such as the shale oils and tight sands requires hydraulic fracture stimulation.
Details of estimating these approximate PPDs can be found in Padhi and Mallick (2014) and Li and Mallick (2015). The dashed curves, shown in Figure 3 denote the search windows used for estimation each model parameter. Notice from Figure 3 that the peaks of these estimated PPDs were connected to obtain an estimate for each model parameter. Also notice although we used a wide window for estimating each model parameter, the estimated PPD functions are very wellconstrained. The sliding window inversion allowed good constraints on the model parameter estimates from shallow to deep, which, in turn, is clearly reflected in these PPD estimates. Figure 2: An example of the 3-component VSP data used in this inversion study.
Accurate microseismic event locations require an accurate velocity model. A common technique for deriving the velocity model involves tomographically inverting perforation shot traveltimes. The approach requires known perforation locations, an initial velocity model and a perf shot aperture large enough to span the velocity medium. In contrast, we developed a velocity modeling approach based on the vertical slowness and polarization angle of microseismic events with unknown locations.
We applied the technique to a microseismic dataset and compared the results with those derived from a tomography-based solution. The slowness-polarization velocity model is very similar to the tomographic velocity model. However, the VTI (vertical transverse isotropy) slowness-polarization velocity model is 16% more like the acquired sonic log in the deeper part of the array.
Presentation Date: Monday, October 17, 2016
Start Time: 1:50:00 PM
Presentation Type: ORAL
Anisotropy parameters provide vital information for surface and borehole seismic data processing, imaging and interpretation. The objective of this research is to introduce a reliable technique, for estimating local seismic anisotropy using both P- and SV-wave from VSP data in VTI media where the overburden is heterogeneous.
The technique uses P- and SV-wave vertical slowness components and polarization angles in VTI media to estimate Thomsen parameter δ and anellipticity parameter ƞ. The proposed method is applied to a synthetic VSP data with anisotropic properties. The estimated δ and ƞ parameters, using both P- and SV-wave data, show better correlation with anisotropy parameters in the model compared to the technique that only uses P- wave data.
Salt rock is characterized by its very low porosity and permeability along with excellent mechanical deformability. These characteristics make it a good cap rock for many structural petroleum reservoirs, a good geological hydrocarbon storage, and a suitable host rock for poisonous and hazardous wastes. Over the past few decades, different laboratory experiments have revealed the complexity and variety of mechanical behaviors of salt rocks. Although the elasto-plastic mechanical properties of salt rock highly depend on its stress state and temperature, but they can also change with its composition. Therefore, different salt rocks around the world show wide ranges of mechanical behaviors and it necessitates more experimental data from different geological regions. In this study 26 rock salt samples, with two different levels of impurities, from the Central Iranian salt rock were collected and examined. A set of rock mechanics experiments, including uniaxial compression test, triaxial compression test, and dipole ultrasonic velocity measurements at elevated temperatures, were fulfilled. It was found that the amount of impurities significantly affect the rock salt mechanical behavior. The results suggest that unconfined compressive strength increases as the temperature increases, but the triaxial compressive strength and the ultrasonic wave velocities demonstrate more complex patterns.
The estimation of seismic velocity is one of the crucial steps for seismic depth imaging in laterally inhomogeneous layers. This task is more challenging for incompetent units overlying the reservoir layer in shallow depth. Gachsaran Formation is a cap rock of the Asmari oil-bearing formation and plays an important role in geophysical studies of Middle Eastern oilfields. According to the complex geological structure and stratigraphy of Gachsaran, which is due to the high tectonic activity of the basin and special lithological and rheological properties of Gachsaran, estimation of seismic velocity is crucial and full of challenges. In the present paper, the relationships between seismic velocity and structural components have been analyzed. The Gachsaran Formation from Aghajari structure (Aghajari oilfield / SW Iran) has been selected for this study. Newly acquired and high quality 3D seismic data provided new insight about the relationships between structural characteristics and seismic velocity.