A Study On Drilling Fluid For Fishbone Horizontal & Multilateral Wells In Jiangsu Oilfield

As a special type of well, fishbone horizontal&multilateral well conbined the technology of slim hole well, directional well and horizontal well. Compare with the drilling fluid used in general vertical wells and horizontal wells, this complicated well need the high quality drilling fluid. According to the higher environmental demands for drilling fluid and its additives these years, we need to study on the formation protection drilling fluid for this special type of well.In order to optimize the formula of the solid-free low gel drilling fluids, the type and appropriate doses of viscosifier, fluid loss additive, shale inhibitive agent, weighting material and bloking agent, compatibility of different additives and the adding sequence of additives should be studied. Through evaluating the performance of drilling fluid, the performance of the rheology, filtration, inhibition, core plugging and formation protection are excellent, even if the solid-free low gel drilling fluid is rolled at 95℃with 24 hours. It has a special rheological property, the ratio of yield value to plastic viscosity is 1.0 Pa/mPa·s; the LSRV is as high as 43800mPa-s; the filter loss and HTHP filter loss are 2.8 mL and 10.8 mL. Three cores with different permeability has been selected to evaluate the recovery value, it is found out in the experiement that the recovery value is as high as 100%with each core, it can meet the requirements for formation damage.In order to selecte the gel breaking methohs for the solid-free low gel drilling fluid and its mud cake removal, the type and appropriate doses of acid, oxidant and enzyme has been studied. A method which conbined enzyme with organic acid has been optimized for the solid-free low gel drilling fluid and its mud cake removal.