A New Approach to Preventing Lost Circulation While Drilling

Abstract

SPE Members Abstract This paper presents a new concept, theoretical formulations, and field test results of the loss prevention material (LPM*) developed for use in many possible applications such as high-angle and horizontal well drilling, drilling through severely depleted formations (to optimize casing requirements), drilling through highly tectonically active areas (i.e., regions of overthrust faults and salt dome structures) where the in situ rock stresses are high and directionally unequal. Both open-hole microfractures and 5000-ft open-hole leak off tests using LPM were successfully conducted in our wells in Newkirk, Oklahoma, and Ventura, California. LPM is a specialty selected (material strength and specific gravity) and narrowly sized granular material which, after being fully mixed in oil or water based mud at an optimum concentration, can provide good protection to formations against lost circulation while drilling. Higher formation fracture resistance resulting from the use of LPM in drilling fluids can reduce or prevent the occurrence of lost circulation while drilling. This paper will show that a remarkable increase of 8.0 ppg in borehole breakdown pressure was achieved in one of our tests in the Newkirk well. An increase of fracture propagation pressure in the range of 3.0 to 6.0 ppg was recorded in the field tests. These results are in general agreement with our laboratory findings also discussed in this paper. Introduction The idea of lost circulation prevention is not only achievable, but also practically feasible. Needless to say, lost circulation prevention is far more cost effective than any remedial action taken after the occurrence of lost circulation. Especially with oil muds, losses can be very expensive, unsafe (underground blowout), and time consuming. It is under this premise that this new LPM (loss prevention material) product was developed for use in "lost-circulation-prone" zones or in high-angle hole drilling when a higher mud weight is required to counter potential borehole collapse, stuck pipe, tight hole, or other hole instability problems. Adding LPM to the drilling fluid will provide the extra margin of borehole protection for mud weights used and will reduce the degree of uncertainty involved with any type of work or operation concerning natural geologic formations. Based on our laboratory test results using large Berea sandstone blocks, an optimum LPM concentration can be found and it varies with mud densities. According to our experimental investigation and analytical verification, formation fracture initiation and propagation during well drilling can be prevented or inhibited by including an effective concentration of LPM (a specialty sized granular material) in the drilling fluid. P. 569^