Lost circulation material formulation and method of use

#1. Field of the Invention

#The present invention pertains to methods and compositions for preventing or alleviating the loss of drilling fluids and other well servicing fluids into a subterranean formation during drilling or construction of boreholes in said formation.

#2. Description of Relevant Art

#According to the prevent invention, an improved lost circulation material (LCM) may be obtained by combining several materials to obtain a composition that has a “bimodal” particle distribution and tolerance to high temperatures. The “bimodal” particle distribution provides sealing of small pores (as small as 190 microns) as well as large fissures (such as 500 to 1000 micron slots). The bimodal particle distribution is obtained by an optimized design of particle types. Adding or coupling a polymer flocculant or a swellable polymer with the composition may extend the utility or enhance the effectiveness of the composition at high temperatures as will be discussed further below.

#The optimized design of the particle types is obtained by adding together the following components: a finely ground fibrous cellulosic material, such as BAROFIBRE® SF material available from Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla., preferably about 35 micron d50, preferably grade “super fine”, and preferably about 5% to about 15% of the composition; resilient graphitic carbon (RGC), such as STEELSEAL® material available from Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla., preferably about 1150 micron d50, preferably about 5% to about 15% of the composition; ground rubber or a biodegradable material such as, for example, ground walnut shells, preferably about 10-30 mesh, preferably about 5% to about 25% of the composition; and diatomaceous earth, preferably about 25 micron d50, preferably about 55% to about 75% of the composition. Ground walnut shells may provide further advantages by being ground into different or bimodal sizes, that is, large or larger and small or smaller sizes, such as, for example, about 410-420 micron d50 (small) and about 1100-1200 micron d50 (large). The dimension d50 (or d10) means that 50% by volume of the particles are smaller than the value indicated.

#Table 1 below demonstrates a bimodal particle size distribution for an example preferred composition of the invention in more detail: