Herman H. Rieke

Chapter 2 Origin of abnormal formation pressures

Publisher Summary Interstitial (intergranular or formation) fluid pressures, either above or below the hydrostatic pressure, occur around the world under a wide range of geological conditions. Any pressure that is either above or below the hydrostatic pressure is referred to as an abnormal formation pressure. Pressures above the hydrostatic pressure are often referred to as abnormally high (AHFP) or surpressures. Pressures below the hydrostatic pressure may be referred to as either abnormally low (ALFP) or subpressures. The object of early formation analysis of abnormally pressured zones was primarily to predict and identify these zones prior to drilling into them. This need for prior knowledge was motivated by the economic losses that were often experienced by suddenly drilling into an unrecognized abnormally pressured region. Attention must be paid to pore fluid and rock stresses in sedimentary sequences, because the knowledge of vertical and lateral stress patterns in a depositional basin is helpful in evaluating its history and development. A thorough quantitative understanding of compaction mechanics, the relationship between the total overburden stress, effective stress, and pore stress (pressure) in fine-grained clastics is required to recognize the potential development of abnormally high-pressured formations.

A Review of the Importance of Gravitational Sediment Compaction in Oil Producing Areas

Abstract During the past quarter of a century, the exploitation of oil and gas reserves, associated with thick sequences of very fine-grained and coarsegrained rocks in the Tertiary Basins, have become increasingly important for fulfilling the worlds energy needs. Many exploration and reservoir development problems have arisen which demand an analytical solution. The solution of many scientific and technological problems associated with these geologically young basin sediments requires knowledge of the origin, maintenance, and distribution of abnormally high pore-fluid pressures, chemical changes induced in the interstitial water by compaction, origin and migration of hydrocarbons, temperature gradients, clay minerals phase changes, and subsidence of the surface. Successful drilling to depths greater than 20,000 ft in these sediments and the amounts of hydrocarbons discovered and produced depend to a great extent on our knowledge of the physical and mechanical properties and deformation characteristics o...

Chapter 10 Pore water compaction chemistry as related to overpressures

Publisher Summary Much has been written in the petroleum geology literature on the geochemical evolution of pore liquids and gases associated with fluid flow systems in recent and ancient sedimentary basins. The dialogues include observations about the origin of interstitial fluids, measurements of the active chemical diagenetic processes, and resulting mass-transport properties, which arise during the development of sedimentary basins. Effects of thermal and chemical factors and the dynamic transfer of fluids within the basins leave imprints on the pore–fluid chemistry and generation of abnormally high- (AHFP) or abnormally low-formation pressures (ALFP). This chapter presents and validates a hypothetical model that explains the differences between the salinities of pore water in sandstones and shales in the gravitationally compacted sedimentary basins of Tertiary age. The explanation presented here is based on two diverse, relative scales of resolution—microscopic (10–2 to 10–4 m) and gigascopic (> 105 m). The gigascopic scale presents evidence from field observations, whereas the microscopic scale focuses on laboratory experiments that dealt with the chemistry of fluids in the pore space. Mathematical and conceptual models are presented and discussed, which support these observations. Additionally, the relevance of the isotopic character of shale pore water is evaluated for this environment.

A computational method for determining segmental and overall geothermal gradients and geothermal heat flow values

A new computational method is presented which calculates geothermal heat flow values and geothermal gradients with more precision than permitted by previously published techniques. The data required are: geothermal temperature at a known depth, mean surface temperature, the rock types in the stratigraphic column and the thermal resistivity values for the different types of rocks. This method is valuable in areas that have no measured gradient values. Basic equation used was the Fourier heat transfer equation Q/A = −1/ρi (∂T/∂x) where Q/A is heat flux in μcal/(cm2 s), ρi is thermal resistivity (°C s cm/μcal) and ∂T/∂x is the x component of the temperature gradient (°C/cm). The thermal resistivity was allowed to vary linearly with temperature ρi = ρio [1 + Ki (T − 30)] where ρi is thermal resistivity of the lithographic segment «ia at a temperature T, ρio is thermal resistivity at 30°C and Ki is the temperature coefficient of thermal resistivity. The procedure consisted of integrating the combined equation for heat flux in terms of temperature dependent resistivity. Two iterative solutions were used to simplify the calculations: exact and approximate. The heat flux for each well was assumed to be 1.0 HFU and segmental temperatures were calculated from the bottom (arbitrarily) up, until a surface temperature was obtained. The calculated surface temperature could then be compared with the mean surface temperature (MST). Correction in the heat flux value was made until the calculated surface temperature and MST agreed. An analysis of three deep Appalachian test wells was made and the results showed the critical importance of lithographic ordering and the temperature dependence of thermal resistivity upon calculated geothermal quantities.

Chapter 4 Smectite-illite transformations during diagenesis and catagenesis as related to overpressures

Publisher Summary For the South Caspian basin, the findings of Buryakovsky et al. can be summarized as follows. (1) Regionally developed abnormally high-formation pressures were encountered onshore of Azerbaijan and offshore of the South Caspian basin. (2) Paleogene to Neogene shales and argillaceous rocks, widespread in the geologic section of Azerbaijan and the South Caspian basin, consist of montmorillonite (smectites), hydromica (illite) and mixed-layered minerals. (3) The incomplete compaction of such argillaceous rocks, even at depths down to 6.5 km, is explained by the comparatively young age, a high-sedimentation rate (up to 1 km per one million years), their great thickness, and incomplete squeezingout of pore water. (4) The montmorillonite content of the Baku Archipelago shales is constant down to depths of 6.5 km, because the formation of secondary montmorillonite from hydromicas predominates over the transformation of primary montmorillonite. (5) A formula was proposed for the limiting depth at which montmorillonite can occur for any specific thermobaric conditions and, particularly, when the actual pore pressure differs from the normal hydrostatic one. (6) The sealing properties of argillaceous rocks at depths greater than 6.5 km probably persist, because of the presence of large amounts of montmorillonite. If accompanied by (1) good reservoir rock properties, (2) abnormally high pore pressures in shales and sandstones, and (3) relatively low-formation temperatures (which allow hydrocarbons to persist), the writers suggest that the South Caspian basin may contain commercial oil and gas accumulations at depths of 9 km, and deeper. (7) Development of abnormally high pore pressures may lead to lateral rock-density variation and, under certain geologic conditions, to folding, clay diapirism, mud volcanism, and earthquakes.

Chapter 8 Tectonics and overpressured formations

Publisher Summary Abnormally high-pore fluid pressures may result from local and regional tectonics. The movement of the Earths crustal plates, faulting, folding, and lateral sliding and slipping, squeezing caused by downdropping of fault blocks, diapiric salt, and/or shale movements, earthquakes, etc. can affect formation pore pressures. Due to the movement of sedimentary rocks after lithification, changes can occur in the skeletal rock structure and interstitial fluids. A fault may vertically displace a fluid-bearing layer and either create new conduits for the migration of fluids, giving rise to pressure changes or create up-dip barriers giving rise to isolation of fluids and preservation of the original pressure at the time of tectonic movement. Sahay noted that this barrier may be created by either the fault itself or by bringing the impermeable layer in contact with the permeable layer up-dip. In strongly folded formations, there is a reduction in pore volume (due to compression) along with an attenuation of competent layers (in limbs) and accumulation in the cores of anticlinal folds. An additional rupturing of layers of formations also takes place due to squeezing of and stretching of the skeletal rock structure beyond its elastic limit. Thus, there is a development of high-fluid pressure in isolated blocks.

Dynamic Fracturing Phenomena in Model Materials Resulting from Shaped Charge Jet Penetration

During the jet penetration process, the compressive wave pulse will decrease in magnitude and the manner of failure in the target material will change as the distance from the jet axis increases. Distinct zones of failure are formed concentrically around the jet penetration axis: plastic zone, zone of small radial fractures, and zone of large fractures. An understanding of the origin of the fracture zones and their time of formation in relation to detonation is necessary before shaped charges can be more efficiently used for well completion. The results of this study indicate that fracture orientation and propagation are not only a function of the charge geometry, but also a function of some physical characteristics of the target material. (19 refs.)