How to manage drill-in fluid composition to minimize fluid losses during drilling operations

Selection of the best drill-in fluid for drilling horizontal wells is essen tially based on the characteristics of the filter cake formed in the near-w ellbore region. Minimizing filtrate loss into the formation by forming a th in filter cake with low porosity and permeability is the key to managing fo rmation damage problems. In this paper, the effects of drill-in fluid components and their interacti ons in the formation of a filter cake, which provides an effective caking p rocess with reduced filtrate loss, have been evaluated. Statistically desig ned experiments carried out with a dynamic filter press apparatus were used to identify which variables had the most significant effect on filtrate lo ss and cake permeability so that the optimum fluid composition could be det ermined. These variables include the formation characteristics (permeabilit y and pressure values) as well as the type and amount of the fluid componen ts. Data obtained in this experimental design study were analyzed with the mult iple-linear-regression method, which allowed us to model the filtrate loss and cake permeability. The analysis showed that the most important factors are the type and the concentration of the polymer. In particular, when the formation temperature is as high as 90 degreesC, we can reduce the cake per meability and the filtrate loss by increasing the concentration of sclerogl ucan. An interaction effect between the concentration of scleroglucan and t he more highly crosslinked starch was also identified, and none of the othe r variables showed any significant effects within the range of experimentat ion. This fact can be considered as an advantage because it allows flexibil ity in the choice of other factors when appropriate for the cost reduction.