The Study and Application of Novel Delayed-Opening Toe Sleeve with Dissolvable Components Towards Long Horizontal Wells

The flow path for hydraulic fracturing is usually generated in the toe position of one long-reached horizontal well by perforation using coiled tubing, which exhibits high deploying risk and operation cost. Some foreign toe sleeves have been introduced to domestic oil and gas fields to form first flow path instead of complicated intervention such as perforation. The drawbacks including expensive service and low reliability have negative effect on large-scale applications of traditional toe sleeves. Research Institute of Petroleum Exploration and Development (RIPED) innovatively developed delayed-opening toe sleeve with dissolvable components. The time-delay controlling component based upon dissolvable alloy will degrade after contacting with down-hole fluids. The pressure test of casing can be performed during degrading of the components and the sleeve can be finally activated to form the flow path between wellbore and reservoir. With the adjusted dissolvability the delay period is able to be modified to meet the demand on customizing pressure test. As one alternative to current technique like perforation, the toe sleeve with dissolvable components exhibits the advantages of high flow rate, high reliability, adjustable time delay and low-pressure specification of embedded rupture discs. The novel toe sleeve performs flow-path opening of the first stage with temperature rating of 150 ℃, pressure rating of 120 MPa and delay-time range of 30–60 min with three different specifications of 4.5 in, 5 in and 5.5 in. The field trials of delayed-opening toe sleeves have been carried out in five wells of unconventional resources so far without any failure in the toe depth. This paper proposed the technique solution of delayed-opening toe sleeve, workbench qualification and field validations in unconventional reservoirs including shale gas and shale oil. Furthermore, future trend of casing toe valves is also put forward in this paper.