Evaluating the Sealing Effectiveness of a Caprock-Fault System for CO₂-EOR Storage: A Case Study of the Shengli Oilfield

Abstract

An effective sealing system is crucial for CO 2 -EOR storage, and these sealing systems are typically composed of the caprocks and faults that surround a reservoir. Therefore, the sealing effectiveness of a caprock-fault system must be evaluated at various stages of CO 2 -EOR storage projects. This paper presents a new evaluation framework that considers specific site characteristics and a case study on the sealing effectiveness of the caprock-fault system in the Shengli Oilfield. The proposed method is a weighted ranking system where a set of 17 indicators has been developed for the assessment and ranking of the G89 block in terms of their sealing ability for CO 2 sequestration. Additional indicators are involved in the method, such as the newly proposed parameter, frontier displacement work which reflects the influence of formation pressure, displacement pressure resistance, and caprock thickness. The new approach considers the sealing mechanisms of caprocks and faults as well as the configuration relationships between them. The method was used to evaluate the sealing effectiveness of the G89 block that has a considerable number of faults and good sealing ability of caprock in the Shengli Oilfield.

A Caprock Evaluation Methodology for Underground Gas Storage in a Deep Depleted Gas Reservoir: A Case Study for the X9 Lithologic Trap of Langgu Sag, Bohai Bay Basin, China

“…Generally speaking, the higher the clay content, the better the sealing capacity, and the mudstone caprock formed by the semi-deep and deep lake facies has the best sealing capacity [10][11][12]. The caprock thickness refers to the effective thickness after subtracting the area with no sealing capacity, and statistics show that there is a thickness lower limit for the sealing capacity, beyond which, the thicker the caprock is, the higher the cap continuity is, the stronger the sealing capacity is, and the larger the gas field area formed [9,[13][14][15]. The rock mechanics sealing mechanism means that in the process of injection and production, the stress state of the caprock will change, leading to the generation of cracks, which further makes the seal invalid.…”

“…Many scholars have noticed the change of brittleness and ductility of mudstone for a long time, and carried out many experiments on mudstone rock mechanics, and defined the evaluation criteria of mudstone brittleness by using different parameters, but there are few studies specifically on mudstone caprock of gas storage [4,16,17]. From the microscopic perspective, porosity, permeability, pore size distribution, specific surface area, and displacement pressure are the main parameters to reflect the microscopic sealing capacity of caprock, among which displacement pressure is widely regarded as the most fundamental parameter that reflects the sealing capacity of caprock [8,13,14,18]. The sealing mechanism of hydrocarbon caprock can be divided into a capillary seal, hydraulic seal, overpressure seal, and hydrocarbon concentration seal, among which capillary seal is the most important sealing mechanism of depleted gas storage caprock.…”

“…The laboratory test of displacement pressure can be divided into the direct method (step-by-step method, continuous method, displacement method, and pulse method) and indirect method (mercury intrusion method), where the step-by-step method is based on the definition of breakthrough pressure and has a high accuracy [11,[19][20][21]. The breakthrough pressure can also be obtained by fitting field data, such as the time difference of acoustic velocity [14,22,23].…”

Coupled Large Scale Hydromechanical Modelling for Caprock Failure Risk Assessment of Gas Storage in Aquifer

“…Current research shows that the mechanical integrity of caprock will be affected by many factors during these processes [24,25]. For example, the injection rate, the initial in situ stress, and the injection temperature have the greatest effects on the mechanical integrity and stability of caprock [26][27][28]. However, there are few reports on the mechanical integrity and stability of caprock under the action of multiperiod alternating injection and production.…”

A Novel Assisted Gas–Oil Countercurrent EOR Technique for Attic Oil in Fault-Block Reservoirs

“…The production mode proposed by Combs and Knezekl [9] was not applicable to fault-block reservoirs in China which are sealed and have lower formation energy without strong water driving [32,33]. In order to recover the attic oil in this type of reservoir, a new modified development mode needs to be established.…”