Restoration of reservoir diagenesis and hydrocarbon accumulation process by calcite in-situ U-Pb dating and fluid inclusion analysis: A case study on Cretaceous Qingshuihe Formation in Gaoquan Structure, southern Junggar Basin, NW China

The complexity of diagenesis and hydrocarbon accumulation in the deep reservoirs in southern Junggar Basin restricts hydrocarbon exploration in the lower reservoir assemblage. The lithofacies and diagenesis of reservoirs in the Cretaceous Qingshuihe Formation in the Gaoquan structure of the Sikeshu Sag, southern Junggar Basin were analyzed. On this basis, the thermal history was calibrated using calcite in-situ U-Pb dating and fluid inclusion analysis to depict the hydrocarbon accumulation process in the Gaoquan structure. The results show that the Qingshuihe reservoir experienced two phases of calcite cementation and three phases of hydrocarbon charging. The calcite cements are dated to be (122.1±6.4) Ma, (14.4±1.0) Ma - (14.2±0.3) Ma. The hydrocarbon charging events occurred at around 14.2-30.0 Ma (low-mature oil), 14.2 Ma (mature oil), and 2 Ma (high-mature gas). The latter two phases of hydrocarbon charging contributed dominantly to the formation of reservoir. Due to the S-N compressive thrust activity during the late Himalayan period since 2 Ma, the traps in the Gaoquan structure were reshaped, especially the effective traps which developed in the main reservoir-forming period were decreased significantly in scale, resulting in weak hydrocarbon shows in the middle-lower part of the structure. This indicates that the effective traps in key reservoir-forming period controlled hydrocarbon enrichment and distribution in the lower reservoir assemblage. Calcite U-Pb dating combined with fluid inclusion analysis can help effectively describe the complex diagenesis and hydrocarbon accumulation process in the central-west part of the basin.

Studies on the Time of Accumulation and Elimination of Alexandrium tamarense Toxins in Argopectens irradias

Using a PSP （paralytic shellfish poisoning） toxin-producing strain of4lexandrium tamarense, it studied the timing of toxin accumulation and elimination of PSP toxins in Argopectens irradias. The PSP toxicity was studied by following the standard PSP mouse bioassay developed by the Association of Official Analytical Chemists （AOAC）. Alexandrium tamarense was cultured to an average density of 1.26 × 10^4/mL for a total of about 50 L culture. The toxicity of the alga was 2.18 ×10^-6 MU/cell. The results show that PSP content increased with time in both visceral and muscle tissue during a two-week accumulation period during which scallops were fed with ,4. tamarense. The average toxin level in scallop＇s viscera was 49.4 MU/g, with an average of 10.0 MU/g in muscle tissue. This level is 2.5 times higher than the sanitation standard （4.0 MU/g of muscles）. The highest value was 61.0 MU/g in the viscera. In summary, the viscera accumulated greater concentrations of toxin than muscle tissue. Scallops that had accumulated toxins were transplanted for two weeks into a field environment containing no toxic algae. The PSP content of the scallops decreased to 7.9 MU/g viscera and 1.6 MU/g muscles two weeks after being transplanted, but did not reach the sanitation standard. Under the experimental conditions, the toxin depuration rate of shellfish toxin was 12% daily. This study worked toward the development of a sanitary shellfish industry and better management of PSP toxin-impacted shellfish in China.

Evaluation of 40^Ar/39^Ar Geochronology of Authigenic Illites in Determining Hydrocarbon Charge Timing： A Case Study from the Silurian Bituminous Sandstone Reservoirs, Tarim Basin, China

The Silurian bituminous sandstones（SBS） in the Tarim Basin, China are important basinwide reservoirs with an estimated area of approximately 249000 km^2. We investigated the ages of authigenic illites in the SBS reservoirs and constrained their formation timing by using the 40^Ar/39^Ar step wise heating method. The age spectra, 39^Ar recoil loss and their controlling factors were investigated systematically. The 40^Ar/39^Ar ages were compared with the conventional K/Ar ages of identical clay fractions. The clay in the SBS reservoirs is dominated by orderly mixed-layer illite/smectite（I/S） with 5%–30% smectite layers. The I/S minerals morphology comprises primarily honeycomb, short filamentous and curved-lath particles, characteristic of authigenic illites. The unencapsulated 40^Ar/39^Ar total gas ages（UTGA） of the authigenic illites range from 188.56 ± 6.20 Ma to 491.86 ± 27.68 Ma, which are 7% to 103% older than the corresponding K/Ar ages of 124.87 ± 1.11 Ma to 383.45 ± 2.80 Ma, respectively. The K-Ar ages indicate multistage accumulations with distinct distribution patterns in the Tarim Basin： older（late Caledonian-early Hercynian） around the basin margin, younger（late Hercynian） in the basin centre, and the youngest（middle to late Yanshanian） in the Ha-6 well-block, central area of the North Uplift. The age difference is believed to have been caused by the 39^Ar recoil loss during the irradiation process. Compared with the K/Ar ages, the estimated 39^Ar recoil losses in this study are in the range from 7% to 51%. The 39^Ar recoil loss appears to increase not only with the decreasing particle sizes of the I/S, but also with increasing percentage of smectite layers（IR） of the I/S, and smectite layer content（SLC） of the samples. We conclude that due to significant 39^Ar recoil losses, UTGA may not offer any meaningful geological ages of the authigenic illite formation in the SBS and thus can not be used to represent the hydrocarbon charge timing. 39^Ar recoil losses during 40^Ar/39^Ar dating can not be neglected when dating fine authigenic illite, especially when the ordered mixed-layer I/S containing small amount of smectite layers（IR30%） in the reservoir formations. Compared with the unencapsulated Ar-Ar method, the conventional K-Ar method is less complicated, more accurate and reliable in dating authigenic illites in petroleum reservoirs.

ACCELERATION AMBIGUITY FUNCTION OF RADAR SIGNALS AND ITS APPLICATION

High acceleration of radar targets is analyzed using Acceleration Ambiguity Function (AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.

A digital time correlative accumulation(Ⅱ)——cross-correlative accumulation

The digital time cross-correlative accumulation ( DTCCA ) scheme is described in the paper. The basic principle and structure of the scheme are discussed first , the detection probability, false-alarm probability and input S/ N are then analyzed for some typical sonar systems . The superior performances have been proved true through theoretical estimations and field experiments . Like DTACA , the DTCCA , as a signal processing scheme , has a wide application in complicated shallow acoustical channel at low data rate.