Stress Sensitivity Assessment Of Tight Sandstone Reservoir

In this paper,the physical properties of the Jia Formation core in this area were analyzed through core observation,gas porosity,and permeability measurement;the petrological characteristics and pore microscopic characteristics of the reservoir were determined by means of casting thin slices,ordinary thin slices,scanning electron microscopy,and X-ray diffraction.3.The microscopic characteristics of clay minerals were analyzed;the structure characteristics of reservoir core pore throat were analyzed by means of mercury intrusion.Conducted experiments of variable confining pressure and variable internal pressure,and evaluation experiments of reservoir sensitivity.Based on the characteristics of the tight reservoir in this area,the mechanism of stress sensitivity and sensitization was studied from multiple angles,and mercury intrusion and stress sensitivity were developed.Contrast experiment,stress-sensitivity comparison experiment of artificially-produced samples and matrix samples,filling and non-filling of cracks,comparison experiments of filling with different fillers,comparison experiments of different connectivity stress-sensitivity,stress-sensitive multiple loading experiments and different water saturation Stress sensitive contrast experiment.This article finally reached the following conclusions:1.The experimental methods of variable internal pressure and variable confining pressure can reflect the stress sensitive damage of the reservoir to a certain extent,but considering the complexity of the reservoir structure in the study area is mostly low porosity and permeability formation,the experiment of variable internal pressure is selected The method better simulates the situation where the actual formation is subjected to stress-sensitive damage due to the net stress.2.The average damage rate in the study area is higher than 85%,which is a strong stress-sensitive.Viewed from the plane,the well area in the central western region shows strong stress sensitivity,and the relatively weak MN well area shows moderately weak to moderately strong.There are slight differences in the three small layers,but the overall performance is still highly stress-sensitive;longitudinally,except for the J1a1 layer to the Jla2 layer in the MN well area,there is a weakening trend.Has not changed much.Therefore,the reservoir as a whole shows strong stress sensitivity,and the central well area shows a moderate to strong to strong irreversible damage rate.3.There are three types of stress-sensitive damage curves in the study area:Medium-speed stress-sensitive damage is accompanied by strong irreversible damage;rapid stress-sensitive damage is accompanied by weak irreversible damage;medium-speed stress damage is accompanied by moderate irreversible damage.4.The research on the mechanism of stress-sensitive damage is mainly on the factors of pore throat,fracture,multiple loading and water saturation,etc.The main factors leading to the stress sensitivity in the study area are micropore development and microfracture development through experiments and geological data.Therefore,this paper mainly studies the damage mechanism of dual media in the two aspects of pore throat factor and crack factor,thus explaining the reasons for generating three types of stress-sensitive damage curves.5.The stress sensitivity is very serious when there are cracks in the tight sandstone.Therefore,in the process of on-site production and development,exhaustive mining should be avoided as much as possible,and the formation energy should be replenished in time to prevent the sharp decrease of reservoir permeability due to the increase of net stress This has led to a reduction in production during the development process.At the same time,avoiding the decrease of reservoir pressure leads to the closure of some fractures in the reservoir,resulting in the decline of fracture connectivity in the reservoir,resulting in a sharp decline in reservoir permeability.The better the fracture connectivity,the stronger the stress sensitivity,so the layer should be maintained The internal pressure is relatively stable,avoiding strong stress sensitivity in well-connected areas and resulting in poor physical properties of the reservoir;at the same time considering the effect of stress sensitivity,it is not recommended to use a large pressure difference during the trial production process,and to reduce or avoid the increase in water saturation The high makes the stress sensitivity of tight sandstone stronger,and attention should be paid to reducing the filtration loss of drilling and completion fluid during drilling and completion,or using drilling techniques such as nitrogen drilling.6.Based on the above situation,this article gives practical suggestions for specific well areas:(micro)fractured wells(such as Ditan 1)due to rapid pressure damage in the early stage of pressure drop,irreversible damage is small,you can take the first failure(critical pressure 6.6MPa)mining,The protective measures to supplement the formation energy in the later period to improve the recovery factor;(micro)pore development-based wells(such as Dibei 102,Tuzi 4,Tuzi 2,Tudong 2,Kezi 1)although the initial stress-sensitive damage rate Small but irreversible damage(38.86%)is not suitable for decompression mining,and early protection measures for supplementing formation energy are needed;wells with(micro)fractures and(micro)pores are well-balanced(eg Yishen 4,Yinan 2,Yinan4,Yinan5)Due to the moderate stress damage speed and irreversible damage in the initial stage of pressure drop,the first step of decompression(original formation pressure of 20%)can be adopted for exploitation,and the protection measures of supplementing formation energy in the medium term.