Abdullatif A. Al-Shuhail

Processing of Seismic Reflection Data Using MATLAB

This short book is for students, professors and professionals interested in signal processing of seismic data using MATLAB. The step-by-step demo of the full reflection seismic data processing workflow using a complete real seismic data set places itself as a very useful feature of the book. This is especially true when students are performing their projects, and when professors and researchers are testing their new developed algorithms in MATLAB for processing seismic data. The book provides the basic seismic and signal processing theory required for each chapter and shows how to process the data from raw field records to a final image of the subsurface all using MATLAB. Table of Contents: Seismic Data Processing: A Quick Overview / Examination of A Real Seismic Data Set / Quality Control of Real Seismic Data / Seismic Noise Attenuation / Seismic Deconvolution / Carrying the Processing Forward / Static Corrections / Seismic Migration / Concluding Remarks

Mapping the internal structure of sand dunes with GPR A case history from the Jafurah sand sea of eastern Saudi Arabia

The study of the geometry and internal structure of modern aeolian deposits (sand dunes) can give a better understanding of sandstone hydrocarbon reservoirs like the A and B members of Unayzah Formation in Saudi Arabia. These members have been shown to contain depositional facies like aeolian dunes, aeolian sand sheets, and interdunes (Melvin and Heine, 2004).

Automated SVD filtering of time-frequency distribution for enhancing the SNR of microseismic/microquake events

Recently, there has been a growing interest in continuous passive recording of passive microseismic experiments during reservoir fluid-injection monitoring, hydraulic-fracture monitoring and fault-movement monitoring, to name a few. The ability to accurately detect and analyze microseismic events generated by these activities is valuable in monitoring them. However, microseismic events usually have very low signal-to-noise ratio (SNR), especially when monitoring sensors (receivers) are located at the surface where coherent and non-coherent noise sources are overwhelming. Therefore, enhancing the SNR of the microseismic event will improve the localization process over the reservoir. In this study, a new method of enhancing the microseismic event is presented which relies on one trace per receiver record unlike other methods. The proposed method relies on a time-frequency representation and noise eliminating process which uses the singular-value decomposition (SVD) technique. Furthermore, the SVD is applied on the matrix representing the time-frequency decomposition of a trace. More importantly, an automated SVD filtering is proposed, so the SVD filtering becomes observation-driven instead of user-defined. Finally, it is shown that the proposed technique gives promising results with very low SNR, making it suitable to locate passive microseismic events even if the sensors are located on the surface.

Improving automatic first-arrival picking by supervirtual interferometry: examples from Saudi Arabia

The objective of this study is to test the feasibility of using the supervirtual seismic interferometry method for improving automatic picking of first arrivals in petroleum seismic data. Fundamentally, interferometry is a mathematical technique used to position virtual sources at the location of actual receivers to gain the power of additional signals utilizing the physics of wavefield reciprocity and time reversal. Supervirtual interferometry extends the technique to far source-receiver offsets having very low signal-to-noise ratios. The benefits gained in more accurate first-arrival picking are significant, especially when near-surface velocity variations are severe and can have a detrimental impact on accurately mapping subtle structures. The supervirtual workflow consists of the following: windowing around first arrivals, cross-correlation, source stacking, convolution, and receiver stacking. The workflow is tested on a 2-D synthetic seismic data. In addition, the workflow has been tested on a 2-D petroleum seismic data from Saudi Arabia with considerable attenuation of first arrivals with offset. Results show that the workflow greatly improves first arrivals at all offsets, particularly at far offsets. Furthermore, testing the effect of a localized continuous random-noise source (e.g., due to machines) on the method’s performance show that such noise does not affect the method’s performance, which might be due to extensive trace mixing by the cross-correlation and convolution operations.

Mapping the surface of a shallow groundwater system using GPR: A case study in eastern Saudi Arabia

The Eastern Province of Saudi Arabia is considered one of the most prolific oil-producing regions in the world. During the last three decades, cities in the province have vastly expanded due to various industrial and urban activities. As a result, a considerable number of developments, including suburbs as well as industrial facilities, have been built on top of sabkhas and sands with shallow groundwater systems. The proximity of shallow groundwater systems to the basement of many structures can influence building foundations and the hydrogeologic environment.

Analysis of microseismic events during a multistage hydraulic stimulation experiment at a shale gas reservoir

Despite the current easing in demand for increased oil production linked to the global downturn in crude prices, energy demand continuously increases and the long-term demand will require maximizing the productivity of reservoirs and a search into the exploitation of new resources in increasingly challenging environments. In this study, we present the results from the monitoring of the very first multistage stimulation experiment at a shale gas reservoir in Saudi Arabia, presenting an analysis of the microseismicity induced during the treatment. Our aim was to analyse microseismic events to better understand fracture growth and the role of pre-existing fractures in these reservoirs. Microseismic (MS) event monitoring is used to track the creation of fractures during and after the stimulation, and therefore to evaluate the effect of the reservoir stimulation. The monitoring includes a downhole array of 12 3C-sensors that were deployed in a vertical well with a 30.5 m level spacing. A total of 415 MS events were located and analysed, with the results outlining induced fractures extending consistently with an average azimuth of N335° E, normal to the horizontal section of the treatment well. This implies that there are no changes in the local stress direction along the treatment well either in situ or induced along the treatment. There are significant changes in total length and aspect ratio (length/width) of the fractures induced in the different stages. These variations could be attributed to in situ fracturing, local rock heterogeneity or the influence of the treatment parameters. In general, early and late stages of stimulation show the longest fracture networks, with events induced further away from the initiation point. We found no immediate relationship between treatment parameters (peak pressure and pumping rates) and fracture extension. Sensitivity analysis using Monte Carlo simulation methods shows a higher location uncertainty for events located at the early stages, thus limiting the interpretation from monitored seismicity in the early stages. An analysis of magnitude distribution with distance shows a decrease in sensitivity of one degree of magnitude for every 375 m, and a maximum viewing distance of approximately 700 m for the current set-up. The low number of located events does not provide a complete enough dataset for a robust analysis of changes in b-value (slope in linear part of magnitude distribution) during the treatment: however, magnitude distributions, corrected for array sensitivity, provide a useful variable for the validation of geomechanical models currently being developed for the reservoir.

Iterative interferometry-based method for picking microseismic events

Abstract Continuous microseismic monitoring of hydraulic fracturing is commonly used in many engineering, environmental, mining, and petroleum applications. Microseismic signals recorded at the surface, suffer from excessive noise that complicates first-break picking and subsequent data processing and analysis. This study presents a new first-break picking algorithm that employs concepts from seismic interferometry and time-frequency (TF) analysis. The algorithm first uses a TF plot to manually pick a reference first-break and then iterates the steps of cross-correlation, alignment, and stacking to enhance the signal-to-noise ratio of the relative first breaks. The reference first-break is subsequently used to calculate final first breaks from the relative ones. Testing on synthetic and real data sets at high levels of additive noise shows that the algorithm enhances the first-break picking considerably. Furthermore, results show that only two iterations are needed to converge to the true first breaks. Indeed, iterating more can have detrimental effects on the algorithm due to increasing correlation of random noise.

Joint Inversion of Ground-Penetrating Radar and Seismic Velocities for Porosity and Water Saturation in Shallow Sediments

ABSTRACT Ground-penetrating radar (GPR) measures the velocity (VG) of electromagnetic waves in a subsurface material. In a low-loss material, VG depends primarily on the porosity (φ) and water saturation (Sw) of the material. Therefore, it is impossible to estimate φ and Sw uniquely from VG without additional information. The seismic P-wave velocity (VP) in the same material can provide the extra information required for the inversion. In this study, an approach is described for a closed-form solution of VG and VP to invert for φ and Sw in shallow sediments. The complex refractive index model (CRIM) for VG and Gassmann-Biot model for VP are used to relate these velocities to φ and Sw. Each model presents a nonlinear equation in φ and Sw. The two equations are solved simultaneously to estimate φ and Sw from VG-VP measurements. Testing of the inversion procedure in the presence of errors in assuming the properties of the soil matrix showed that these errors can drastically affect the inverted water saturati...

Fracture-porosity inversion from P-wave AVOA data along 2D seismic lines: An example from the Austin Chalk of southeast Texas

Vertical aligned fractures can significantly enhance the horizontal permeability of a tight reservoir. Therefore, it is important to know the fracture porosity and direction in order to develop the reservoir efficiently. P-wave AVOA (amplitude variation with offset and azimuth) can be used to determine these fracture parameters. In this study, I present a method for inverting the fracture porosity from 2D P-wave seismic data. The method is based on a modeling result that shows that the anisotropic AVO (amplitude variation with offset) gradient is negative and linearly dependent on the fracture porosity in a gas-saturated reservoir, whereas the gradient is positive and linearly dependent on the fracture porosity in a liquid-saturated reservoir. This assumption is accurate as long as the crack aspect ratio is less than 0.1 and the ratio of the P-wave velocity to the S-wave velocity is greater than 1.8 — two conditions that are satisfied in most naturally fractured reservoirs. The inversion then uses the fra...

Using Ground-Penetrating Radar to Delineate Fractures in the Rus Formation, Dammam Dome, Eastern Saudi Arabia

Ground-penetrating radar (GPR) has been used recently to detect many near-surface geological features in arid regions. In this study, GPR is used to delineate near-surface fractures within the Dammam Dome. This anticlinal structure covers ~160 km2 and hosts the first oil well discovered in Saudi Arabia. Doming is due to the buoyancy of the Hormuz Salt. Rock units present within the dome range in age from Paleocene to middle Miocene. Well-developed fractures crosscut the dome and extend for several km. Our results prove that GPR techniques can be used successfully to map precisely near-surface open and filled fractures. This technique is demonstrably useful for environmental, engineering, and geological studies.