Qingcheng Oilfield is located in the southwest of Ordos Basin in China. Its main production layer is the tight sandstone in the source of the Chang7 reservoir of Yanchang formation. At present, the proved geological reserves are about 35.5 ∼ 40.6°108t. However, due to the tight physical properties of the reservoir (the permeability of overburden matrix is usually less than 0.1md, the porosity is less than 10%), the low pressure coefficient of the original reservoir (0.7-0.8) and the strong heterogeneity of lake facies sedimentation, the conventional vertical well is affected the production of single well is very low, and the large-scale development of horizontal well becomes an effective technical way. The development practice of horizontal wells with volumetric fracturing in Qingcheng oilfield shows that the average initial production of single well can be increased from 8.5t/d to 18.6t/d by effectively increasing the length of horizontal section (the length of horizontal section increases from 800–1000m to 1500–2000m, and the rate of oil layer drilling is 78%). At the same time, the large platform and factory integrated mining mode can effectively solve the well site construction and maintenance costs of the complex landform of the Loess Plateau sensitive to the environment. With the development of horizontal wells as one of the main technologies of economic scale development in Qingcheng oilfield, it is more and more urgent to further increase the length of horizontal section to increase the single well production to a greater extent.

Well #H50-7 is an ultra-long horizontal well in Chang7 source reservoir of Qingcheng oilfield, with a designed horizontal section length of 4000m. The area where the well is located has complex structure, developed faults, great changes in horizontal reservoir buried depth, and great differences among wells. Conventional technology cannot find the reservoir in time and accurately and ensure the well trajectory to pass through the reservoir, which is not conducive to improving the oil layer drilling rate and reservoir productivity evaluation of explored horizontal wells after well completion. Based on the combination of 3D stochastic modeling technology, reservoir engineering theory and numerical simulation method, through the establishment of pre-drilling geological model, real-time interpretation of logging data while drilling, timely geological guidance, well trajectory description and optimization, the top boundary and landing point depth of the target layer are effectively determined. The vertical depth is 1973m, the vertical ratio is more than 2.0, the maximum offset is 155m, and the horizontal section is 4088m. The drilling and completion technology of offset distance and three-dimensional horizontal well in long horizontal section has achieved 75.6% of the drilling rate of oil layer in horizontal section, and achieved good geological guidance and trajectory control effect.

This technology effectively solves the geological tracking and optimization adjustment in the process of horizontal trajectory while drilling a complex structure and thin inter-bed reservoir, makes the horizontal well production technology of tight reservoir more complete, and realizes the large-scale development of Chang7 reservoir in Qingcheng oilfield.

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