The Characteristics And Evolution Of Hydrodynamic Force And Their Effect On Hydrocarbon Accumulation In Kuqa Foreland Basin

The foreland basin experienced strong tectonic compression. Tectonic stress field have an intensly transformation effect on fluid pressure field in strong active stage. All these make the composition and evolution and distribution of hydrodynamic force in main history period complicated, which need deepen the hydrocarbon migration and accumulation rule on this background. The Kuqa foreland located in south Tianshan experienced strong tectonic compression from the Tianshan in the Himalaya later period and is the ideal study area for research on the relationship between hydrodynamic force and hydrocarbon accumulation of foreland basin. The region was taken as the key object to analyse in this paper, and hydrodynamic force evolution and distribution characteristics of main accumulation stage and their relationships with the hydrocarbon accumulation in this region were researched, in order to further understand hydrocarbon migration and accumulation rule of foreland basin.The genetic mechanism of abnormal high pressure in foreland basin under the influence of some factors were researched in this paper by the comprehensive utilization of drilling, well logging, mud logging, analysis and test and so on, the previous research results. The assessment new method of pressurization according to tectonic compression in real strata conditions or semi-enclosed systems is advanced, and the ancient and modern tectonic overpressure was quantitatively estimated by the comprehensive utilization of finite element numerical simulation and multifactorial comprehensive evaluation. Constrained by such direct evidences as ancient and modern pressure, the depoditional overpressure in different geologic periods were reconstructed by use of numerical simulation analysis technique. The gas potential or gas potential gradient in different geologic periods was further restored on this basis of fluid pressure restoration. The relationship between hydrodynamic force and hydrocarbon accumulation in the key accumulation stage was analysed combined with the reservoir-formed stages research result and the known hydrocarbon distribution at present and the favorable exploration region were predicted. Lastly accumulation model acted on by hydrodynamic force in foreland basin were probed on the whole, and pointed out the key problems during the foreland hydrodynamic force research.The result of research show that:(1) The overpressure of reservoir in the Kuqa foreland basin result from the effect of disquilibrium compaction, in combination with later tectonic compression and overpressure transference. The overpressure according to the disquilibrium compaction contribution to excess pressure have the difference in differenent region, is gengerally 15% to 30% in the Kelasu region and 4% to 22% in Dina and Dabei region; (2) Tectonic overpressure effect at the conditions of the true strata has also relation with the system sealing degree except for the lateral compressive stress strength and the depth. The stronger system sealing degree become, the bigger tectonic overpressure become under the same compression background. Tectonic compression is strongly intensive in Kuqa foreland basin in the Himalaya later period, and tectonic overpressure effect is most obvious. But the amplitude of tectonic overpressure are great difference between the tectonic positions, is bigger in Kelasu region and secondly in Keshen and Dongqiu region and relativly smaller in Dabei and Dina region and none in Tabei Uprift; (3) The hydrodynamic force in foreland basin chang obviously at different stages. The vertical gas potential gradient become bigger on the whole, increased 1 and 2 times after the strong tectonic compression in the Himalaya later period, which greatly enhance the vertical migration force. The plane gas potential gradient become bigger in the most area, and smaller in the local area, respectively enhance and weaken lateral hydrocarbon migration force. On the whole, the hydrodynamic force reach its highest value in the strong tectonic compression stage and fluid flow is also most active; (4) The diffenent tectonic positions in foreland basin have the difference migration and accumulation characteractics after the strong tectonic compression. As for strong compression region, the strong tectonic compression makes the relatively lower potential fault zones becoming the fluids concourse nearby in the strata and make the vertical hydrodynamic force bigger greatly at the same time. The concourse fluids near the fault zone migrate towards upper strata along the opening fault because of the gypsum-salt caprock sealing and charge the lateral sand, accumulate in the ralatively low potential area lastly. As for weak compression region, the oil and gas laterally migrate under the strong hydrodynamic force along the sandsone and the unconformity, accumulate in the ralatively low potential area in the sandstone lastly; (5) The later hydrodynamic force has an important control effect on hydrocarbon distributions in the foreland basin. The later hydrodynamic force control the accumulation and the lacation of hydrocarbon, and low potential backgroud of the later hydrodynamic force and the low potential gradient of the migration direction control the accumulation. The strong migration force greatly increase the hydrocarbon accumulation efficiency of the hydrocarbon migration direction region.