The coupling of dynamics and permeability in the hydrocarbon accumulation period controls the oil-bearing potential of low permeability reservoirs:a case study of the low permeability turbidite reservoirs in the middle part of the third member of Shahejie

The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such types of reservoirs can form hydrocarbon accumulation with high accumulation dynamics; however, reservoirs with diagenetic facies A and diagenetic facies B do not develop accumulation conditions with low accumu- lation dynamics in the late accumulation period for very low permeability. At more than 3000 m burial depth, a larger proportion of turbidite reservoirs are oil charged due to the proximity to the source rock, Also at these depths, lenticular sand bodies can accumulate hydrocarbons. At shallower depths, only the reservoirs with oil-source fault development can accumulate hydrocarbons. For flat surfaces, hydrocarbons have always been accumulated in the reservoirs around the oil-source faults and areas near the center of subsags with high accumulation dynamics.

Dynamic Field Division of Hydrocarbon Migration,Accumulation and Hydrocarbon Enrichment Rules in Sedimentary Basins

Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins： at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins （i.e., depths of around 1000 m）, hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil （-gas）-water inversion, indicating that the oil （gas） accumulated under the water. However, the oil （gas） tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena： a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%-12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation： the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as ＂four high,＂ indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as ＂four low,＂ indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil（-gas）-water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs： there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.

Analysis of Dynamic Accumulation of Three Types of Glutenin Subunits and Their Content in Relation to Sedimentation Value in Common Wheat

The biosynthetic time and accumulations of A-, B-, and C-type glutenin subunits in 7 winter wheat cultivars with different quality （strong, medium, weak gluten） were analyzed by SDS-PAGE. The results showed that no glutenin subunit was observed within 8 d after anthesis. Parts or all A-, B-, and C-type subunits appeared around day 12 in different cultivars. Other A-, B-, and C-type subunits appeared gradually. The accumulation of A-, B-, and C-type subunits fluctuated before maturity. The results of analysis of correlation between the ratios of A/T （total content of glutenin subunits）, A/C, AJ （B＋C）, （A＋B）/C, and （A＋B）/T and SDS-sedimentation value suggested that they were more significant. The negative correlation between the ratio of （B＋C）/T and SDS-sedimentation value was more significant, and the correlations between the ratio C/T and the SDS-sedimentation value were significantly negative.

Dynamics of Nutrient Accumulation in Maize Plants Under Different Water and N Supply Conditions

The dynamics of accumulations of plant dry matter, nutrient uptake and N fertilizer recovery were studied with different water and N supply, using summer maize (Zea mays L. var. Shandan9) as an indicator crop. The total dry matter (including roots) and N, P, K uptake amounts were continuously increased with plant growth, and their accumulations with time during plant-growing period were shaped in S curves that could be described by exponential regression equations. Differentiating the regression equations fitting the curves over time for first derivatives, the momentary rate was obtained of the dry matter and nutrient uptake. Results show that the dry matter and the nutrient uptake were not in the same rate at all time, but changed from one time to another. Usually, the rate increased rapidly at early stages, and gradually decreased after reaching their peak. Of N, P and K, the uptake rate of N and K was higher, and their increase and decrease were both fast while P was reversed. The time of the maximum absorptive rate appeared earlier for K, followed by N, and then by P. In any case, the maximum nutrient uptake rate appeared earlier than did the dry matter. The momentary N recovery rate was similar in trend to those of dry matter and N uptake, and its maximum recovery rate occurred almost at the same time as its maximum uptake rate. Supplemental irrigation raised the cumulative and momentary rates of N. Although water and N supplies increased dry matter and nutrient uptake rates, they did not alter their changing trends during the plant-growing period.

Dynamic Systems of Petroleum Accumulation in the Nanpu Depression,Bohai Bay Basin,China

It is significant to distinguish the dynamic systems of petroleum accumulation （DSPA） for the understanding of petroleum accumulation and distribution. According to the formation pressure framework, genetic types of petroleum and characteristics of conduit systems, three dynamic systems of petroleum accumulation were identified in the vertical profile in the Nanpu depression, Bohai Bay basin. The deeper DSPA （including formations Es3 to Es2） is a sealed system with high-overpressure and high-mature self-sourced oil. Most of the crude oil in the system accumulated in the periods of late Oligocene （23.5 Ma） and late Pliocene （2.4 Ma）. The middle DSPA （including formations Es~ to Edl） is an overpressured half-sealed system with mature or lower-mature self-sourced oil. The accumulation of oil in the system also occurred in the late Oligocene （23.5 Ma） and late Pliocene （2.4 Ma）. The shallower DSPA （including formations Ed2 to Q） is a hydrostatic system with lower-mature aliensourced oil from the middle system. Oil within this system accumulated only in the late Pliocene period. The oil in the shallower system migrated vertically along the faults from the formerly accumulated oil in the middle system by lateral migration along the sandbodies, whereas petroleum accumulation in the deeper system was mainly derived from the system itself by lateral migration along the sandbodies and rarely migrated out of the system. In this case, it seems that the deeper system is a more potential exploration prospect in addition to the other two proved favorable systems.

Dynamic stress accumulation model of granite residual soil under cyclic loading based on small-size creep tests

The creep behaviors of granite residual soil with pre-stress of 100 kPa was investigated by a series of small size creep tests. Three different types of strain curves were obtained at different stress levels. Based on creep characteristics of the granite residual soil under different stress levels, a creep model of the granite residual soil was established by rheological theory, and related parameters of the model were determined according to the experimental data at the same time. Further on, based on the established creep model, a theoretical model of dynamic stress accumulation in the granite residual soil under cyclic loading was deduced. It is found that there is a threshold of dynamic stress accumulation in this theoretical model. The dynamic stress accumulation laws of the granite residual soil are different under different cyclic loading stress. Finally, with the dynamic stress accumulation laws in the small-size samples of granite residual soil under different cycle loading studied and the experimental results comparing with the theoretical results, it verifies the validity of the theoretical model.

Variations in Carbohydrate and Protein Accumulation among Spikelets at Different Positions Within a Panicle During Rice Grain Filling

The accumulation dynamics of kernel components for spikelets at different positions within a rice panicle were investigated during grain filling to understand the physiological reasons for the variation of grain quality.Two rice cultivars,Yangdao 6 （indica） and Yangjing 9538 （japonica）,were field-grown,and the grain filling characters and contents of starch,soluble sugar,and protein of the spikelets at different positions were studied.There were significant differences in matter accumulation among spikelets at different positions during grain filling.The early-flowering spikelets presented dominance over the late-flowering spikelets in initial time and initial rate of accumulation.At the initial and mid filling stages,the contents and the rates of starch and amylose accumulation in spikelets decreased with the flowering sequence,but soluble sugar content （SSC） exhibited the opposite trend.The difference in SSC among the spikelets of Yangjing 9538 was greater than that of Yangdao 6,but amylose content in mature spikelets showed no obvious relationship to their flowering sequence.The crude protein content （CPC） of early-flowering spikelets decreased more rapidly than that of late-flowering ones at the initial filling stage,and CPC in the spikelets on the secondary branch was higher than that on the primary branch,but CPC in early-flowering ones was lower than that in late-flowering across the whole grain filling period.Grain water content （GWC） of early-flowering spikelets decreased more rapidly than that of late-flowering spikelets on the same branch at the initial and mid filling stages,especially for the top grain on each primary branch.The results suggested that poor grain filling of late-flowering spikelets may be attributed to their low biological activity rather than carbohydrate supply limitation.

Long-term dynamic behavior of monopile supported offshore wind turbines in sand

The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.

Mechanism of petroleum migration and accumulation in western China's superposed basins

In western China, most petroliferous basins are superposed due to their multi-periodic tectonic evolution, and the mechanisms of petroleum migration and accumulation are so complex that much more sophis- ticated methodologies are necessary for depiction of these mechanisms and identification of petroleum occurrences. For this purpose, in this article, a new methodology was formulated which includes： （I） ver- tical identification of petroleum migration and accumulation fluid dynamic systems in the superposed basins; （2） analysis of the effect of large scale regional faults and fault combinations on the fluids exchange between the vertically identified different systems; （3） analysis of petroleum migration and accumulation in each vertically identified system, and establishment of appropriate geological model of petroleum migration and accumulation for each vertically identified system. Using this methodology, the satisfactory results obtained in the Lunnan Uplift of Tarim Basin and Ludong Uplift of Jungar Basin case studies are： （1） existence of different vertical fluid dynamic systems in western China＇s superposed basins which are very necessary for understanding the mechanism of petroleum migration and accumu- lation; （2） in deep system, long-distance lateral petroleum migration and accumulation mainly take place along the long time exposed unconformity with weathered, fractured or karst reservoir rocks; （3） regio- nal faults are the main conducts for fluids migration from deep system up to middle and/or upper sys- tems. As to middle and/or upper systems, regional faults play a role of ＂petroleum source＂. Small faults within middle and/or upper systems conduct petroleum to carrier beds with less impeding force; （4） petroleum migrated from deep system vertically up to middle and/or upper systems will migrate lat- erally in carrier beds of these systems and accumulate to form nools near or far from faults.

Comparative Analysis of Sequence Characteristics among Different Superimposed Stages of the Chelif Basin,Algeria

Superimposed basins were investigated with respect to tectonic evolution, sediment deposition and petroleum characteristics within a single superposition stage generally. The comparative study was seldom seen. Sequence characteristics were compared for two different superimposed stages - an expanding rifting stage and a depression-foreland transition stage - in the Chelif Basin during the Miocene in this paper. A model and mechanism for sequence evolution of superimposed basins in different dynamic situations are discussed with respect to sequence similarities and differences. The compared characters include sequence thickness, sequence boundaries and system tracts, as well as sediment deposition within sequences and sequence development patterns. Finally, some typical features of sequence development concomitant with changes of superimposed stages in the Chelif Basin are discussed.

Accumulation conditions and key technologies for exploration and development in Sebei gas field in Qaidam Basin,NW China

The Sebei gas field,located in the northern slope of the Sanhu depression in the eastern Qaidam Basin,is the largest inland biogas producing area in China.It is a typical Quaternary biogenetic gas reservoir composed of multiple layers of unconsolidated sandstone.Through systematic study of gas generating mechanism of source rock,reservoir-caprock combination and trap evolution,the unique biogas accumulation model characterized by“continuous hydrocarbon generation and dynamic accumulation”is established.Its uniqueness is reflected in the biogas generation mechanism under dual effect of lowtemperature thermodynamics and microbial degradation,source-reservoir one body,self generation and self storage,dynamic source-reservoir-caprock assemblages and anticline trap formation mechanism of multi-factor mutual promotion.This understanding reveals the intrinsic factors for formation of largescale biogas field under frigid climate,high salinity and low organic matter abundance.A number of exploration and development technologies have been worked out during the exploration and development of the Sebei gas field.Among them,the low-amplitude structure identification technique,multiparameter gas-bearing detection technique,sand control and comprehensive water control technique for unconsolidated sandstone are well applied in discovering the gas field,increasing reserve,and increasing and maintaining gas production.The above understandings and key technologies have great reference significance and demonstration effect for biogas exploration and development in China and the world.