Laboratory Study on the Properties of a New Delayed Expansion Lost Circulation Material

Severe mud losses into fractured formations seriously restrict the efficient development of oil and gas in formations with complex geological conditions. Bridging agents presently used for mud loss control have poor deformability, the commonly used water-adsorbing resin lost circulation materials (LCMs), on the other hand, have expansion rates that are too fast, therefore, it is difficult for these LCMs to form dense pressure-bearing barriers in the channels through which the mud is lost into the formations. To solve this problem, a new delayed expansion LCM SDSAP was developed. SDSAP has a density of 1.52 g/cm³ and particle sizes between 0.425 mm and 3.35 mm which are adjustable according to the rate of mud loss. It has excellent water-adsorbing expanding performance, pressure resistance and salt resistance capacity. When water is adsorbed, SDSAP becomes deformable, and is therefore suitable for control mud losses in loss channels with wide range of sizes. SDSAP has a certain delayed expansion effect and low rate of expansion at ambient temperatures. It also has temperature-response property; when excited by high temperatures in downhole condition, it swells quickly, which is beneficial to shorten the time required to seal off the loss channels and thus reduces the amount of mud lost. An LCM slurry formulated with SDSAP and other LCMs such as rigid, elastic LCMs and fibers to stop mud losses into fractures with opening sizes of 1-3 mm. The barrier formed by the LCM slurry had pressure bearing capacity of more than 7 MPa, and the amount of mud lost was greatly reduced. It can be used to solve mud losses into complex fractured formations.