气体欠平衡钻井技术在气田钻井生产的应用

随着气体欠平衡钻井技术在元坝气田开发中的应用,这种技术不仅在提高机械钻速、延长钻头寿命、减少地层损害有作用,石油行业也期盼气体欠平衡钻井技术在环保方面发挥重要作用。

Characteristics of late cretaceous faults of the eastern segment of the northern Qaidam basin, NW China

The Late Cretaceous tectonic upheaval was an important event during the evolution of the Qaidam Basin, resulting in the omission of the Upper Cretaceous in the whole basin and unconformities between the Paleogene sequence and pre-K2 strata. Inte-grating geological and geophysical data, two different groups of Late Cretaceous faults were recognized in the study area, one group consisting of E-W extending strike-slip faults (e.g., the Maxian and Yema-Jinan faults in the Mahai area, which caused an E-W omission zone of Mesozoic), while the other one has NW-SE thrust faults, resulting in NW-SE fold-and-thrust belts. Considering the different strikes and scale of these two groups, a simple-shear model has been employed to explain this structural phenomenon. The NW-SE thrust faults were thought to be subsidiary to the E-W strike-slip faults. Putting this into the framework of the Cretaceous paleogeographic environment of central Asia, it is inferred that this tectonic event of the Qaidam Basin is a response to the continuous northward drifting of the India plate.

Offshore Multi-Wave Seismic Exploration in Bohai

In Oilfield A, of south Bohai, the large area (20km^2) of gas in the shallow layer of the main structure makes a "gas cloud" effect in the seismic section. It makes the seismic migration imaging of the deeper aim layer inconsistent with the actual features of a geologic structure. But, the converted waves,PS waves, containing effective information of incident compressed (P) waves, can create converted S waves. The S wave is affected little by the shallow layer screen, allowing better imaging of the deeper layer. So, 4C seismic acquisition was carried out on the structure. Through geologic reconnaissance on the site, shallow layer drilling analysis and multicomponent seismic experiments, the offshore acquisition flows are designed. Choosing appropriate processing flows for converted waves and paying attention to the key tache of processing, a high quality 2D converted wave section was obtained. By identifying the character of the seismic wave correctly, making use of the full wave logging, producing synthetic converted wave seismogram, and identifying horizon, we can carry out structure interpretation and reserve evaluation of the oilfield.

Exploration and Study on Deep Crust Structural Characteristics in the Jiashi-Artux Seismic Region

The data from two deep seismic sounding profiles was processed and studied comprehensively. The results show that crust_mantle structures in the investigated region obviously display layered characteristics and velocity structures and tectonic features have larger distinction in different geological structure blocks. The boundary interface C between the upper and lower crust and Moho fluctuate greatly. The shallowest depths of C (30 0km) and Moho (45 5km) under Jiashi deepen sharply from Jiashi to the western Kunlun mountain areas, where the depths of C and Moho are 44 0km and 70 0km, respectively. The higher velocity structures in the Tarim massif determine its relatively “stable” characteristics in crust tectonics. The phenomenon in the Jiashi region, where the distribution of earthquake foci mostly range from 20km to 40km in depth, may infer that the local uplift of C and Moho interface, anomalously lower velocity bodies and deep large faults control earthquake occurrence and seismogenic processes in the Jiashi strong earthquake swarm.

Study on Active Faults in Quaternary Unconsolidated Sediments by Microstructural Method

Active faults in Quaternary unconsolidated sediments are important indicators to determine paleoearthquake events. They can be studied by macroscopic geological survey, but some problems have been encountered, such as invisible active faults. The authors found an approach to solve these problems by microstructural observation. Firstly, oriented original-state samples of Quaternary unconsolidated sediments in active fault zones are collected. Secondly, the samples are consolidated in laboratory. Thirdly, microstructural slides are ground in three-dimension coordinate system. Lastly, microstructures are observed in the microscopic field. By this method, the movement properties of active faults can be determined in lack of the support of macroscopic data. The invisible faults in Quaternary unconsolidated sediments can be found and described. The mechanisms of die-out faults can be also studied. Moreover, the boundaries between different unconsolidated sediments in engineering sites can be studied to judge whether they are active faults or not.

Discussion on the Seismogenic Fault of the 1976 Tangshan Earthquake

The opinions of two papers carried in the journal "Seismology and Geology" are discussed in the paper.One is that the Tangshan fault is a high-angle,west-dipping and thrust with strike-slip fault.The other is that the Fuzhuang-Xihe fault distributed on the east side of Tangshan city is the seismogenic fault that caused the Tangshan earthquake.For the former opinion,it needs to explain the relationship between the active style of the thrust Tangshan fault and the formation genesis of a Quaternary depression along the west side of Tangshan city.For the latter opinion,if the Fuzhuang-Xihe fault is the seismogenic fault of the Tangshan earthquake,it needs to explain the genesis relationship between this west-dip slip fault zone and the strike-slip surface fissure zone that extends through Tangshan city.And it needs more evidence exclude the possibility that the surface rupture belongs to the rupturing of a secondary structure.This paper suggests doing more work on the active fault that controls the Caobo Quaternary depression.

Structural feature and tectonic evolution of Awati-Bachu area in Tarim Basin

The research area is situated in the western part of Tarim basin,which includes Awati depression and Bachu uplifted block. It underwent three times processes of compression in a large scale and a near term extension since Cambrian. The first compression occurred during Middle Cambrian to Devonian, which formed fault band folds in NW axial direction. They were "under-water uplift"and distributed all over the research area. The second compression occurred in Late Permian and formed fault band folds and a few fault propagation folds in NS axial direction. They are developed near Tumuxiuke fault belt and the northern research area. The western anticline is bigger than the eastern one in extent and size. The third compression occurred during Palaeogene to Quaternary and formed tumuxiuke fault belt and fault propagation folds in NW direction. They are distributed over the south part of the research area. Tumuxiuke fault belt is a big scale dextral reversed strike-slip fault belt; it transformed or destroyed the fold structure of the research area. A short-term extension occurred during Early Permian. Tarim Basin is in the rift forming stage of craton, and there exist widespread basic volcanic rocks, basic intrusive bodies and dikes.

Site Earthquake Characteristics and Dynamic Parameter Test of Phase Ⅲ Qinshan Nuclear Power Engineering

The earthquake characteristics and geological structure of the site to sitting the Qinshan Nuclear Power Station are closely related. According to site investigation drilling, sampling, seismic sound logging wave test in single-hole and cross-hole, laboratory wave velocity test of intact rock, together with analysis of the site geological conditions, the seismic wave test results of the site between strata lithology and the geologic structure were studied. The relationships of seismic waves with the site lithology and the geologic structure were set up. The dynamic parameters of different grades of weathering profile were deduced. The results assist the seismic design of Phase Ⅲ Qinshan Nuclear Power Plant, China.