«PIERCE JUNCTION SALT DOME, TEXAS -A Thesis Presented to the Faculty of the Department of Earth and Atmospheric Sciences University of Houston In ...»
3-D SEISMIC SURVEY DESIGN VIA MODELING AND REVERSE TIME MIGRATION:
PIERCE JUNCTION SALT DOME, TEXAS
the Faculty of the Department of Earth and Atmospheric Sciences
University of Houston
----------------------------------------------------------------------------------In Partial Fulfillment of the Requirements for the Degree Master of Science
----------------------------------------------------------------------------------By Suleyman Coskun University of Houston May, 2014 i
3-D SEISMIC SURVEY DESIGN VIA MODELING AND REVERSE TIME MIGRATION:
PIERCE JUNCTION SALT DOME, TEXAS______________________________________________
Dr. Robert Stewart (Chairman) ______________________________________________
Dr. Shuhab Khan (Member) ______________________________________________
Dr. Edip Baysal (Member) ______________________________________________
Dean, College of Natural Sciences and Mathematics ii
Shuhab Khan for his support and comments.
My sincere thanks goes to Dr. Edip Baysal for his invaluable guidance and assistance in the preparation of this research. I would also extend my gratitude to Dr. Orhan Yilmaz and Irfan Tanritanir for their great support at Paradigm.
I also acknowledge companies Paradigm, GEDCO, and Geosoft for technical and software support. Texas Brine Company is also thanked for giving AGL the unique opportunity to work in their facility. I sincerely thank the Turkish Petroleum Corporation (TPAO) for financially supporting me throughout my study.
I thankmy fellows in University of Houston: Omer Akbas, Unal Okyay, Kenan Yazan, Sercan Pisen, Gokhan Kose, Eray Kocel, Ozbil Yapar, and all AGL members for their alltime support for this research.
I wish to express my great gratitude to my parents, Edip and Sehnaz Coskun, and my brother Gokhan Coskun for their understanding, support, and encouragement.
Finally, and most importantly, it is difficult to find words to express my gratitude for my beloved wife, Selin Deniz Coskun. Her support, encouragement, quiet patience, and
Basic seismic survey design parameter calculations are generally useful to image flat layers and slightly dipping surfaces. However, parameter decisions for surveys over complex structures, such as folds, faults, domes, and reefs become more challenging due to complicated wave field behavior in these areas. In this study, another seismic survey design decision method, acquisition design via imaging, is presented using the Pierce Junction salt dome as an example. Pierce Junction is one of the most prolific fields in Texas. Depths of the top of the salt and its overlying cap rock are about 290 m and 210 m, respectively.
Previous studies, 2-D seismic, topography, and gravity data were gathered to build 2-D and 3-D velocity models of the Pierce Junction salt dome area in the south of Houston, Texas. Two-D seismic data acquired by Allied Geophysical Laboratories (AGL) were processed and velocities of the cap rock and near-surface sediments were extracted. Also, 2-D gravity data were collected with 200 m intervals from an 8 km-long gravity profile in study area. The gravity data were processed and modeled in order to be used in 3-D velocity model. Then, a series of analyses were performed on synthetic seismic data to determine 2-D conventional seismic survey parameters that can be achieved with limited acquisition equipment of AGL. Shot gathers were modeled with a finite difference method using the full (two-way) acoustic wave equation. Next, to generate images, Reverse Time Migration (RTM) method was applied to the synthetic data. The optimum parameters of
proposed that a 2-D seismic survey with 20 m group interval, 40 m shot interval, 3000 m maximum offset, 4 s recording time, and 8 km profile length parameters was able to image the salt dome and surrounding sediments adequately.
The optimum parameters of the 2-D survey were modified for a 3-D seismic survey.
Survey dimensions and patch definition were determined by the help of obtained 2-D survey parameters. Group and shot intervals were slightly increased to 25 m and 50 m, respectively. The receiver and shot line intervals were determined as 250 m. An orthogonal geometry was chosen due to its cost effectiveness and spatial continuity advantages over the other survey geometries. Eventually, 33 in-lines and 33 cross-lines were uniformly distributed to 8 km by 8 km survey area. Aspect ratio of the patch was kept as 1:1 with 13 in-lines and 13 cross-lines. After determining the final 3-D survey parameters, RTM images were obtained based on the 3-D velocity model. As a result, the final images including cross sections and depth slices showed that the salt dome and its surrounding sediments were adequately imaged with the 3-D survey using Reverse Time Migration analysis.
CHAPTER ONE: INTRODUCTION
1.1 Motivation and Scope
1.2 Structural Framework of U.S. Gulf Coast
1.3 Fundamentals of Salt Dome Geology
1.3.1 Salt Dome Formation
1.3.2 Fault Systems around the Salt Domes
1.3.3. The Cap Rock
1.4 Thesis Organization
CHAPTER TWO: DATA AND METHODS
2.1 Study Area
2.2 Total Station Survey
2.3 2-D Seismic Data
2.3.1 Seismic Data Acquisition
2.3.2 Seismic Data Processing
2.3.3 Seismic Interpretation
2.4 Gravity Modeling
2.4.1 Gravity Data Acquisition
2 Gravity Data Processing
2.4.3 Forward Modeling and Interpretation
CHAPTER THREE: ACQUISITION MODELING FOR THE PIERCE JUNCTION SALT DOME.... 50
3.1 Velocity Models
3.2 2-D Seismic Survey Design via Modeling and RTM Imaging
3.2.1 Fundamentals of 2-D Seismic Survey Design
3.2.2 Analyses of the Actual 2-D Survey
3.2.3 2-D Seismic Survey Design using RTM Cases
3.2.4 Analyses of the 2-D Survey with Optimum Parameters
3.3.2 3-D Seismic Survey Design using RTM Cases
CHAPTER FOUR: DISCUSSION
CHAPTER FIVE: LIMITATIONS OF THE STUDY
CHAPTER SIX: SUMMARY AND CONCLUSION
1.1 Motivation and Scope A seismic project is comprised mainly of data acquisition, processing, and interpretation.
The survey design and acquisition somehow determine the quality of processing and interpretation. Even the best processing techniques cannot reveal good results from the data that have some insufficiencies in acquisition. Therefore, processing and interpretation should be considered in survey design and acquisition part of a seismic study.
The goal of designing seismic surveys is to balance the cost of the survey and imaging needs of the interpreter. Expenses, equipment demands, and time limitations of the surveys force geophysicists considering the survey parameters by taking both economical, logistical, and technical parameters into account. A good survey design can be possible by gathering as much information as possible from the survey area.
Stone (1994) summarized two important survey objectives that should be kept in mind while planning a seismic survey as: (1) Primary objective to obtain geophysical data that provide a representation of the subsurface geology that is adequate to meet the interpretational goals, and (2) Secondary objective to acquire the maximum amount of data within budgeted funds and time available.
Acquisition parameters calculated by general survey design formulas are usually adequate to image flat layers and slightly dipping surfaces. However, determining these parameters for complex structures, such as folds, faults, domes, and reefs is more difficult due to complicated wave field behavior in these areas. Seismic data acquisition simulations over a model of the study area can provide crucial information for determining the survey parameters. If the model is constructed close enough to the real structure, it is possible to obtain very realistic synthetic seismic data using seismic modeling. Therefore, seismic modeling is one of the most economical ways to establish and test the optimum acquisition parameters so as to get the best image over the complex geological structures.
The Pierce Junction salt dome is one of the hundreds of salt domes in U.S. Gulf Coast.
Besides oil and gas production, brine production and underground hydrocarbon storage facilities are established in the field. The brine producing caverns are operated by drilling the edge of the salt dome. Adequately imaging the salt dome flanks can reduce the risk of natural disasters such as sinkholes and hydrocarbon seepage. A 2-D seismic study was carried out in the Texas Brine Company facility by Allied Geophysical Laboratories (AGL).
New 2-D and 3-D seismic surveys were also proposed since the original 2-D seismic data can only image a portion of the top of the salt. The motivation of this study is to investigate the feasibility of additional 2-D and 3-D seismic surveys for imaging the salt dome flanks and surrounding sediments by AGL’s limited equipment.
The scope of this study is to provide a seismic survey design decision method by an acquisition modeling study using the Pierce Junction salt dome area as an example. TwoD and 3-D velocity models of the area were built as close to the real environment as possible and survey design parameters were determined by updating the initial survey parameters with finite difference modeling and Reverse Time Migration (RTM) images.
1.2 Structural Framework of U.S. Gulf Coast The Gulf of Mexico Basin is an elongated structural basin with a length of about 1,500 km.
As shown in Figure 1.1, the offshore part of the basin comprises the Gulf of Mexico which covers an area of more than 1,500,000 km2 (Salvador, 1991). The abyssal plain ( 3000 m deep) constitutes 20% of the Gulf while, the continental shelf ( 180 m deep), continental slope (180-3000m deep), and shallow and intertidal areas ( 20m deep) comprise 20%, 22%, and 38% of the Gulf, respectively (Gore, 1992).
The offshore area of the basin is bounded by a low coastal plain to the north and west.
The low coastal plain is less than 50 km wide in east-central Mexico and more than 550 km wide in the central part of the United States Gulf Coastal Plain, including the states of Louisiana, Mississippi, and Arkansas. Gulfward limits of the shallow parts of the Florida and Yucatan platforms were formed along the Florida and Campeche escarpments where the floor of the Gulf of Mexico rises steeply to the east and south.
The limits of the Gulf of Mexico Basin are defined by existence of the structural features (Figure 1.2). The southern and eastern limits of the basin are estimated to be the Yucatan and Florida carbonate platforms, respectively. The foot of the Chiapas massif, the Sierra Madre Oriental of Mexico, and the eastern edge of the Coahuila platform, forms the western limit of the basin. The northern limit of the basin corresponds to a series of structural features. These features, from west to east, are the basinward flanks of the Marathon uplift, the Ouachita orogenic belt, the Ouachita Mountains, the Central Mississippi deformed belt, and the southern reaches of the Appalachian Mountains. The limit between Appalachian Mountains and the eastern limit of the basin is arbitrary, since no apparent structural feature separating the shores of the Atlantic Ocean and Atlantic Coastal Plain is observed (Salvador, 1991).
Figure 1.1 Location and structural limits of Gulf of Mexico Basin (modified after Salvador, 1991) Figure 1.
2. Second-order structural features within Gulf of Mexico Basin: 1, Macuspana basin; 2, Villahermosa uplift; 3, Comalcalco basin; 4, Isthmus Saline basin; 5, Veracruz basin; 6, Cordoba platform; 7, Santa Ana massif; 8, Tuxpan platform; 9, Tapica-Misantla basin; 10, Valles-San Luis Potosi platform; 11, Magiscatzin basin; 12, Tamaulipas arch; 13, Burgos basin; 14, Sabinas basin;
15, Coahuila platform; 16, El Burro uplift; 17, Peyotes-Picachos arches; 18, Rio Grande embayment; 19, San Marcos arch; 20, East Texas basin; 21, Sabine uplift; 22, North Louisiana salt basin; 23, Monroe uplift; 24, Desha basin; 25, La Salle arch; 26, Mississippi salt basin; 27, Jackson dome; 28, Central Mississippi deformed belt; 29, Black Warrior basin; 30, Wiggins uplift; 31, Apalachicola embayment; 32, Ocala uplift; 33, Southeast Georgia embayment; 34, Middle Ground arch; 35, Southern platform; 36, Tampa embayment; 37, Sarasota arch; 38, South Florida basin (modified after Salvador, 1991).
The Cenozoic tectonic history of the basin is dominated by salt-related deformation in the Gulf of Mexico. Basinward and landward dipping normal faults, contractional folds and different types of salt structures are the major elements of the salt-related deformation (Figure 1.3). Eight river systems draining into the northern Gulf of Mexico basin, the Norma, Rio Grande, Carriso, Corsar, Houston, Red River, and Central and Eastern branches of the Mississippi River, loaded the sediment in the coastal zone, along with continental shelf and slope (Konyukhov, 2008). Salt flow activity began with the differential loading and gliding the major elements of the driving force of salt flow. A variety of complex structures were formed by deformation caused by the salt flow. A block diagram illustrating schematic shapes of salt structures is shown in Figure 1.4.
Structural elements and salt structures that cause salt-related deformation in the Gulf of Mexico (modified after Konyukhov, 2008).