Deep High Pressure Research Articles

Study on Durability of Cement Soil under Brine Erosion

In the coastal areas, deep mixing method or high pressure jet grouting method are usually used to form cement soil during the ground treatment. It’s easy to inflict corrosion damage of cement soil when the underground confined water is connected to the brine. Therefore, research of the cement soil’s durability under the brine erosion is of important significance to engineering. Start from the theory of chemical dynamics and damage mechanics, based on the chemical reaction formula between MgCl2 and the cement soil, with appropriate assumption, the relationship between ion concentration and corrosion time is deduced: (C1/C2)β=t2/t1, that is: when the soil eroded to equivalent mechanic effect, the relationship of corrosion time can be obtained in the solution with high and low concentration. Based on stress strain relationship, incorporate chemical damage factor into compression modulus, suggest certain assumptions, the same relationship between corrosion time and ion concentration is deduced.

Study on Durability of Cement Soil under Brine Erosion

In the coastal areas, deep mixing method or high pressure jet grouting method are usually used to form cement soil during the ground treatment. It’s easy to inflict corrosion damage of cement soil when the underground confined water is connected to the brine. Therefore, research of the cement soil’s durability under the brine erosion is of important significance to engineering. Start from the theory of chemical dynamics and damage mechanics, based on the chemical reaction formula between MgCl2 and the cement soil, with appropriate assumption, the relationship between ion concentration and corrosion time is deduced: (C1/C2)β=t2/t1, that is: when the soil eroded to equivalent mechanic effect, the relationship of corrosion time can be obtained in the solution with high and low concentration. Based on stress strain relationship, incorporate chemical damage factor into compression modulus, suggest certain assumptions, the same relationship between corrosion time and ion concentration is deduced.

Comparative Study of Magmatism in East Pacific Rise Versus Nearby Seamounts: Constraints on Magma Supply and Thermal Structure Beneath Mid‐ocean Ridge

Abstract:Major elements of 2202 basalts from the East Pacific Rise (EPR) and 888 basalts from near‐EPR seamounts are used to investigate their differences in magma crystallization pressures and mantle melting conditions. Crystallization pressure calculation from basalts with 5.0wt%<MgO<8.0wt % shows that magma crystallization pressures beneath near‐EPR seamounts are positively and negatively correlated with Na8 and Fe8, respectively. However, these correlations are indistinct in axial lavas, which can be explained by chemical homogenization induced by extensive mixing processes. In each segment divided by major transforms and over‐lapping spreading centers (OSCs), near‐EPR seamount lavas have higher magma crystallization pressures, higher Fe8 and lower Na8 than the EPR lavas, which indicate cooler lithosphere, lower degrees and shallower melting depths beneath near‐EPR seamounts than the EPR. The correlations between magma crystallization pressures and melting conditions beneath near‐EPR seamounts imply that the source thermal state controls the melting degree and melt flux, and then melting process controls the shallow lithosphere temperature and magma crystallization depth (pressure). The cooler mantle sources beneath near‐EPR seamounts produce a lower degree of melting and a less robust magma supply, which results in a deep thermal equilibrium level and high magma crystallization pressure. The magma crystallization pressure decreases significantly as spreading rate of the EPR increases from ∼80 mm/year in the north (16°N) to ∼160 mm/year in the south (19°S), while this trend is unobvious in near‐EPR seamounts. This suggests that the magma supply controlled by spreading rate dominates the ridge crust temperature and magma crystallization depth, while the near‐EPR seamount magma supply is not dominated by the axial spreading rate. Because most seamounts form and gain most of their volume within a narrow zone of 5–15 km from ridge axis, they provide good constraint on magma supply and thermal structure beneath the EPR. High magma crystallization pressures in seamounts indicate dramatic temperature decrease from the EPR. The crystallization pressures of seamount lavas are well correlated with mantle melting parameters but in a blurry relationship with axial spreading rate. Despite the adjacency of the EPR and nearby seamounts, the thermal structure beneath the near‐EPR seamounts are controlled by their own magma supply and conductive cooling, chemically and thermally unaffected by magmatism beneath the ridge axis.

Deepwater Gulf of Mexico Development Challenges

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 113011, "Deepwater Gulf of Mexico Development Challenges Overview," by Frank Close, Bob McCavitt, SPE, and Brian Smith, Chevron North America E&P Company, prepared for the 2008 SPE North Africa Technical Conference and Exhibition, Marrakech, Morocco, 12–14 March. The paper has not been peer reviewed. A high-level review of recent development challenges for the deepwater and ultradeepwater fields in the Gulf of Mexico (GOM) is presented. How these challenges were addressed and how Chevron plans to address even-more-demanding challenges in the future are summarized. Introduction Operating in all areas of the world presents many challenges. The GOM, although a long-established and prolific hydrocarbon basin, has, over the past 15 or so years, evolved into an arena where operations challenges have been encountered in ever-increasing water depths further from the coast. These challenges include seismic acquisition, drilling operations, completion operations, subsea operations, production operations, logistics support, and many more. Fields are being developed in the GOM that pose the greatest engineering challenges that the company has addressed. It is anticipated that developing resources in water depths of 10,000 ft will be fundamental to the continued long-term success of the GOM as one of the world's major producing basins. Challenges Many of the prospects in the ultradeep-water GOM have a unique combination of challenges. The combination of deep water (to 10,000 ft water depth), high pressure (>10,000 psi shut-in pressures), high temperatures (>350°F bottomhole temperature), problematic formations (e.g., salt or tar zones), deep reservoirs (more than 30,000 ft true vertical depth), tight-sandstone reservoirs (<10 md), and fluids with extreme flow-assurance issues separates many GOM deepwater and ultradeepwater wells from deepwater and ultradeepwater wells in other parts of the world. As Fig. 1 shows, much of the prospective GOM deepwater exploration area is in 4,000 to 10,000 ft of water. Most of this area is in a subsalt environment, with salt canopies ranging from 7,000 to 20,000 ft thick and target depths ranging from 25,000 to 35,000 ft true vertical depth. The vast salt zones inhibit deep-seismic resolution, presenting great challenges in exploration, appraisal, and development operations. Understanding the geology associated with the massive salt and, more importantly, the quality of imaging below the salt is paramount. A key technology being developed to address this challenge is wide-azimuth-towed-streamer technology. This technique allows better subsurface imaging for effective reservoir management and will dictate well placement and number of wells required to drain the reservoir optimally. The true vertical depths of some deepwater wells are in excess of 34,000 ft. Fig. 2 shows some of the drilling challenges.

Key challenges to realizing full potential in an emerging giant gas province: Nile Delta/Mediterranean offshore, deep water, Egypt

The Nile Delta is an emerging giant gas province with proven reserves of approximately 42 × 10 12 SCF. This resource has more than doubled in the last three years, largely from successful deep water exploration for Pliocene slope-channel systems. Proven reservoirs vary in age from Oligocene through Pleistocene. Source rocks include Jurassic coals and shales and the Lower Miocene condensed Qantara Formation shales. Additional source rocks may be present in condensed intervals of Cretaceous, Oligocene and Eocene age. Following Tethyan rifting and opening of the Mediterranean in the Jurassic, prominent Cretaceous mixed clastic and carbonate shelf edges aggraded vertically along a steep fault-bounded shelf-slope break (the ‘hingeline’) in northern Egypt, which exerts the fundamental control on reservoir distribution in Tertiary age strata. In late Eocene time, northern Egypt was tilted toward the Mediterranean during regional uplift associated with the opening of the Gulf of Suez and Red Sea rifts. Drainage systems shed reservoir quality sediments northward in a series of forced regressions. These regressions culminated in be-heading of the youngest deltas by subaerial erosion during the Messinian salinity crisis. Early Pliocene transgressions laid a thick sealing interval over the low-stand Messinian valley networks. Renewed deltaic deposition began at approximately 3.8Ma. The steep structural hingeline and faulted continental shelf created a large amount of accommodation space with relatively minor progradation of depositional systems. As a result, the primary play consists of slope-channel fairways in all levels. The Pliocene systems are the shallowest targets in the basin and future large reserve growth will come from the pre-Messinian strata. Nile Delta gas resources lie close to emerging and established markets in the Mediterranean. Challenges to capturing the deeper pre-Messinian prize include: establishing favourable economic terms for export and domestic markets; reducing drilling costs and optimization of wellbore patterns to develop multiple stacked objectives; working in deep water and high pressure environments; developing predictive models for pressure regressions in overpressured reservoir fairways; recognizing and exploiting thin bedded low resistivity pay.

Overpressuring mechanisms in the Yinggehai Basin, South China Sea

Yinggehai Basin is an elongate Cenozoic rift basin on the northwestern margin of the South China Sea continental shelf. Its thick (17 km) basin fill is characterized by high geothermal gradient and high overpressure. Overpressure associated with nonequilibrium compaction mainly occurs at depths more than 2800 m at the basin center and more than 4000 m at the basin margin because the shallow-buried Neogene and Quaternary strata lack effective seals. This regional overpressure distribution, however, is disrupted at basin center where high overpressure occurs in permeable formations at a depth as shallow as 1400 m on top of a series of deep-seated faults and fractures. We studied the processes and mechanisms of overpressuring via numerical modeling that couples basin filling, sediment compaction, and thermal and pressure fields to approach the origin of the shallow high overpressure. Model results indicated that an increase of fluid volume due to natural-gas generation by organic cracking is not large enough to generate the overpressure because of the limited amount of organic matter. The shallow overpressure has probably been generated allogenically. Deep open faults have served as vertical hydraulic conduits and channeled the deep high pressure into shallow permeable formations.

Phase-controlled molecular fractionations in migrating petroleum charges

Abstract An experimental approach has been used to make a preliminary examination of the possible effects of partitioning processes distributing molecular markers between vapour and liquid petroleum phases during petroleum migration in the system gas-saturated oil/condensate-saturated gas. These effects are discussed with reference to several traditional petroleum geochemical parameters. Some source and maturity related geochemical parameters are dispersed from the inherited source values when a petroleum system undergoes a transition from a single phase gas-condensate to a two phase system and it is probable that partitioning is one of the many processes that contribute to the scattered data sets observed in natural systems particularly those associated with gas/condensates. In addition to affecting gross composition and gas and gasoline range composition, physical partitioning of petroleum components between vapour and liquid phases in deep reservoirs containing rich gas condensate vapour and a liquid petroleum phase in equilibrium can affect even high molecular weight components, selectively partitioning lower homologues into the vapour phase. This may disperse to various degrees any source inherited signature in source facies or maturity interpreted from parameters such as aromatic hydrocarbon distribution, gasoline range parameters, or sterane carbon number distribution. Migration history, or the frequency and extent of multiple equilibrations between vapour and liquid phases in deep high pressure reservoirs followed by selective release of one phase to a shallower position to produce a two phase petroleum system is proposed as an important variable in the geochemical interpretation of once equilibrated petroleum systems. It is concluded that phase related effects must be considered in addition to accepted source and maturity considerations as controlling the molecular composition of two-phase petroleums derived from single-phase precursors. This is particularly so for rich gas condensate systems.

Deep supercooling and high pressure as approaches to cryopreservation

Deep supercooling and high pressure as approaches to cryopreservation