Shale, as a kind of brittle rock, often exhibits different nonlinear stress-strain behavior, failure and timedependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10 −6 s −1 to 1×10 −3 s −1 . The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate-dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut-off point and considering damage variable evolution, a new measure of micro-mechanical strength is proposed. Based on the Lemaitre's equivalent strain assumption and the new measure of micro-mechanical strength, a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.

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Water-swellable packer (WSP) is used rather than oil-swellable packer (OSP) for open-hole packer-sleeve (OHPS) fracturing and completion in China. In this paper, the two improved WSPs including hybrid external casing packer (ECP) and WSP with corrugated packing element are developed to solve the problem of tripping and deployment in irregular horizontal wellbore. The hybrid ECP combines mechanical-set packer with water-swellable packing element. The WSP with corrugated packing elements makes structure more compact than the traditional packer. The two solutions were successfully evaluated by bench test. The former combines the feature of high-rating sealing performance, instant fracturing operation with swelling-assistant isolation. The latter has advantages of smaller size, high reliability and easy tripping over traditional WSP. During OHPS multistage fracturing trial in Sulige gas field, the first five-stage operations are performed with hybrid ECPs and the last two-stage fracture diversion treatment are performed with new WSPs. The fracture diversion was carried out by injecting temporary plugging agents (TPA). The sealing effectiveness is fully validated by long-time ambient pressure differential during fracture diversion. It is shown from field operation that the new OHPS based on improved ECPs is able to meet the requirements of completion and stimulation in irregular horizontal wellbore for tight sandstone reservoirs.