Distribution Prediction of High Overpressure in Jurassic Moxizhuang-Yongjin Area, Central Junggar Basin

doi:10.19657/j.geoscience.1000-8527.2022.205

Abstract

Abstract:

Prediction of abnormal formation pressure is a hot issue in oil and gas exploration and drilling engineering. For the areas with low exploration degree and few exploration wells, the unclear pore pressure distribution characteristics would hamper oil and gas exploration and efficient drilling execution. Therefore, the prediction accuracy of pore pressure needs to be improved. In this study, based on the static equilibrium principle of formation pores, a new pore pressure prediction model based on grain stress is established according to the actual geological data and pressure test data of Yong-Mo area in the central Junggar Basin. The results show that: (1) the classical pressure prediction model has defects. The Terzaghi model is not in static equilibrium, and effective stress is not the actual support force of grains, but a man-made physical variable; (2) we established the pore static equilibrium equation by using the grain stress parameters of porous medium. By comparing the prediction of overpressure of drilling wells in the local deep Jurassic sequences, we found that the pressure prediction accuracy based on grain stress is improved; (3) The pressure prediction model only considers the internal dynamic factor (i.e.deposition supercharging), and overpressure origin compensation cannot be ignored. We found that the local tectonic compression in the southern basinal margin has transferred to the basin interior, and formed the overpressure component with regular distribution. The compensation of additional tectonic stress is an effective way to improve the overpressure prediction accuracy.

Key words: central Junggar basin, pore pressure prediction, static equilibrium, grain stress, overpressure origins compensation

CLC Number:

TE122

HAN Hongwei, LIU Zhen, MA Xinruo, LI Hongmei, HE Yangyang, XU Zeyang. Distribution Prediction of High Overpressure in Jurassic Moxizhuang-Yongjin Area, Central Junggar Basin[J]. Geoscience, 2022, 36(04): 1074-1086.

Figures/Tables 17

Fig.1 Location map of the study area

Fig.2 Measured pore pressure profile of Yong 1 and Yong 6 wells

Fig.3 Measured pore pressure profile of Zheng 1 and Zheng 101 wells

Fig.4 Measured pore pressure profile of Zhuang 1 and Zhuang 3 wells

Fig.5 Relation between porosity and depth, and relation between pore pressure and depth

Fig.6 Equivalent model of porous rock static balance

Fig.7 Relation diagram between rock density and depth

Fig.8 Scatter plot of density and acoustic time in the study area

Fig.9 Relation between shale porosity and depth

Fig.10 Relation between grain stress and depth

Table 1 Calculation results and errors of pore pressure

井号	埋深 /m	实测压力 /MPa	预测压力 /MPa	绝对误差 /MPa	相对误差 /%
永1	6 161.3	113.526	69.903	43.623	38.40
	6 115.25	87.825	70.974	16.851	19.20
	6 090.75	101.5	73.267	28.233	27.80
	5 880.75	97.45	66.58	30.87	31.70
征1	4 810.5	62.05	62.3	-0.25	0.40
征1	4 792.7	60.57	57.97	2.6	4.29
庄1	4 325.7	42.732	44.263	-1.531	3.59

Fig.11 Pore pressure prediction of single well

Table 2 Comparison of strata pore pressure calculated results and errors

井号	实测压力 /MPa	岩石静力平衡方程		等效深度法
井号	实测压力 /MPa	预测压力 /MPa	相对误差 /%	预测压力 /MPa	相对误差 /%
永1	113.526	69.903	38.43	63.80	43.80
	87.825	70.974	19.19	72.43	17.53
	101.5	73.267	27.82	70.13	30.91
	97.45	66.58	31.68	59.83	38.61
征1	62.05	62.3	0.40	67.74	9.17
征1	60.57	57.97	4.29	53.57	11.56
庄1	42.732	44.263	3.58	40.73	4.69

Fig.12 Decomposition diagram of overpressure mechanisms

Fig.13 Compensation pattern by overpressure origins

Fig.14 Distribution of overpressure compensation by stress in study area

Fig.15 Pore pressure prediction of Jurassic in study area

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