Lecture 1: Introduction to Geophysics PDF

Geophysics Department of Oil and Gas University of Thi Qar/ College of Engineering 2022-2023 Ahmed Jalal Fakher Al- Bahar Book 1 Book 2 Geology & Geophysics  Geology: it is an observational science. It involves the study of the earth by...

Geophysics Department of Oil and Gas University of Thi Qar/ College of Engineering 2022-2023 Ahmed Jalal Fakher Al- Bahar Book 1 Book 2 Geology & Geophysics  Geology: it is an observational science. It involves the study of the earth by direct measurements of rock properties, either from surface exposures (outcrops) or from boreholes, tunnels, and mines.  Geophysics: applies the principles of physics to the study of the earth, for deducing physical features of the earth’s surface and its internal structure. Geophysics involves the study of those parts of the earth hidden from direct view, by measuring their physical properties, with appropriate instruments on or above the surface of the earth, remotely from the measurement targets.  Methods Physical property Suitable for Geological structure, spatial variation in Gravitational attraction, Gravity Density contrast rock types: for example, salt domes, shale diapers, reefs and cavities Magnetic ores, Geometry of basement Magnetic field variation, below the sediments, sedimentary cover Magnetic & Electromagnetic Magnetic susceptibility thickness, contrast geological structures and archeological studies Changes in electric Shallow near- surface lithology changes, Electric & Electromagnetic conductivity and or Ground water, cavities permittivity Refraction (Shallow) Travel time to acoustic Engineering problems boundaries, amplitude Seismic (elastic moduli and Geological structure, depositional density contrast), history, faults, rock layers, reservoir size, Reflection (Deep) absorption, velocity shape porosity, pressure, saturation distribution Radiometric Radiation intensity Radioactive ores Geological structures, Shallow salt Geothermal Temperature domes, Anticlines and Fissures Ground Penetration Electromagnetic waves Channels, Cables, Caves, Pipes, Radar - GPR intensity River floor Reservoir, drilling and production engineers  They must be able to understand the information provided by geophysicists, geologists, and petrophysicists so as to be able to properly utilize it. This is particularly important because of the multidisciplinary nature of the challenges faced in oil and gas exploration and production. The need to integrate the data and the disciplines is important.  As engineers become more familiar with geophysical techniques, there will be expansion in applications of geophysical techniques in reservoir engineering practices. During a reservoir’s life cycle from discovery and development to production and field maturation, the needs for reservoir description change continuously. ❑ Date from geophysical tools provide coverage with a spatially continuous high sampling density of 10-25 m and a vertical resolution of the order of 10-20 m. ❑ well data such as cores and well logs provide a vertically high resolution of the order of 0.5 m or better at the well location; however, the distribution of wells is sparse and discontinuous. The detailed spatial coverage from geophysical data is calibrated with analysis of well logs, pressure tests, cores, geologic depositional knowledge, and other information from appraisal wells.  Core R-xxxx R-x R-xx R-xxx Vsh EEI30 EEI40 EEI50 Vsh EEI30 EEI40 EEI50 Vsh EEI30 EEI40 EEI50 Vsh EEI30 EEI40 EEI50 South Rumaila Rock Property Wells Package 1 Top AB – Base F Package 2 Top L2 – Base N Package 3 MSM10 Well logging Seismic reflection & well log Lithology Volume: inline 1703 through Ru-xx well location AB - F LMN MSM10 Geophysical tools and techniques Geophysical methods use high-precision sensors (e.g., geophone, hydrophone, magnetometer, gravity-meter) that measure the physical properties onshore and offshore, in wells and from air, there are also measurements from satellites.  Surface: seismic reflection 2D, 3D, 4D magnetics, gravity, electromagnetics.  Borehole: vertical seismic profiling (VSP), cross well seismic, cross well electromagnetics, microseismic, borehole gravimeter (BHGM), nuclear Geophysics in drilling The process of drilling an oil or gas well requires knowledge of all geologic Static model features expected to be encountered along the way- from the surface of the ground to Seismic & model structures don’t the target reservoir. Thus, in addition to match steering the well so as to intersect hydrocarbon- bearing reservoirs, the reservoir engineer must ensure that the Mishrif seismic surface well drills successfully and safely to the target formations. Update static model with structure interpreted on 3D seismic By providing a picture of the subsurface from the surface to the target, geophysical measurements help ensure a successful drilling program. This geophysical picture helps to: 1. Identify drilling hazards that may lead to an uncontrollable well; 2. Describe construction hazards; predict what lies ahead of and around the drill bit; and 3. Illuminate what exists above and below the well bore in a horizontal or highly deviated well.  Seismic section with Interpreted Horizons W E Dammam Top Rus Top Tayarat Sadi Top Mish Top Ahmadi Top Uppershale N Top YRB peak trough W E S Video