The Design And Application Of Repositionable Pre-stressed Earth Anchor Of Cementing

This paper focuses on the repositionable pre-stressed earth anchor and its application in well cementing. The repositionable pre-stressed earth anchor is a kind of casing tool used for pre-stressed cementing of thermal recovery well, which can satisfy the need of heavy oil thermal recovery and make up the deficiencies of the former pre-stressed cementing technique. Cyclic steam injection technique is commonly used in the recovery of heavy oil reservoir. As a result of high temperature, the casing in the well will expand and elongate, therefore leading to tremendous compressive stress, which can cause the distortion, breaking of the casing, ascending of the wellhead or even well abandonment. Pre-stressed cementing is a kind of technique which a stress is applied on the casing string in the well before solidification of the cement slurry (generating pre-stress in the casing). This technique can decrease or counteract the elongation of the hot casing and avoid damage to the well. To apply pre-stress, the bottom of the casing must be anchored firmly. Earth anchor is a kind of tool used to secure the bottom of the casing. As practice proved, pre-stressed cementing technique can satisfy the requirements of steam injection thermal recovery of heavy oil. By using the pressure differential caused by the flowing action of drilling fluid and its lifting effect to the casing string, the anchor can go effect and solve the problem of the"capacity of going upward and downward"of the casing for the pre-stressed cementing, ensuring the success rate of the operation. When the earth anchor is run into the well, the anchor grippers are in a shrinking position in the anchor body. When the casing is run to the planned depth, the anchor jaw opens, and the tip of the anchor grippers are supported by the wall of the borehole. At this time the casing is lifted upward and then the grippers can enter into the borehole wall, realizing anchoring. If cementing is unsuccessful with the earth anchor, casing can be picked up to change the anchor by stopping the pump and retracting the anchor grippers. Compared with other pre-stressed cementing tools and techniques, the anchor tool and its cementing technology are innovative and have 7 remarkable features. Through laboratory tests, field tests and applications, pre-stressed cementing requirements have been met, providing theoretical and practical basis for further study on cementing with downhole anchor tools. Till present, about 100 sets of anchor tools have been used in Shengli, Henan and other oilfields, creating remarkable technical, economic and social benefits."KFYDM—1100B Earth anchor for Pre-stressed Cementing"was given the third-class award for scientific and technological progress by Shengli Oilfield. The patent right for utility model was granted to"A Borehole Wall Gripping Device for Pre-stressed Cementing"in the name of the above earth anchor.