A water breakthrough warning system of high-yield wells in fracture-cavity reservoirs in Tahe Oilfield

Abstract

A water-out warning system is set up by using water breakthrough data of high yield wells, summing up warning parameters of water-out, and combining with influencing factors of water-out. During the development of Ordovician karst-cave and fracture-vug reservoirs in the Tahe Oilfield, bottom water goes through four stages: prior water invasion, cone period, supporting cone period and breakthrough period. In the late period of the supporting cone, bottom water leads to pressure oscillation in the dissolved cave system, which affects the bottom-hole pressure to some extent. According to the nodal analysis theory, the change of bottom-hole pressure will lead to changes of wellhead pressure, and abnormal signals such as abnormal bottom-hole flowing pressure, tubing pressure, casing pressure, or output. According to geological, engineering, production management factors, and abnormal signals before water-out, 31 indices for water-out risk evaluation are summed up, and early water breakthrough warning technique for high-yield wells is established. Application of the technique to 146 no-water high-yield wells shows the warning technique works well and extends the water free production period. Key words: Tahe Oilfield, fractured-vuggy reservoir, high-yield well, abnormal signal, water-breakthrough warning mechanism