Study and Application of Positive Sol Drilling Fluid

Abstract

SPE Member Abstract This paper reports a new drilling fluid system—positive sol drilling fluid (PSDF). The electrokinetic behaviour, rheological properties and the ability to inhibited clay swelling of positive sol (PS) and PSDF were studied. It was found that PSDF might form weak negative system and positive system under different conditions, and the gel strength and rheological parameters of PSDF could also be adjusted to meet drilling technology demands by changing the ratio of clay-sol. Both PS and PSDF demonstrate high inhibition ability, and PSDF can be treated with conventional additives. In this paper, the field test results of PSDF are introduced as well. Introduction As the methodical study on drilling fluids properties and mechanism of borehole stability was undertaken, Importance of electrokinetic properties of drilling fluids came to be realized. Clay particles possess negative charges, the electrostatic repulsive interaction between negatively charged clay particles increases with increasing negative charges, thus promoting dispersion, which don't benefit penetration and borehole stability. All traditional drilling fluids are negatively charged systems, some anionic additives used, such as FCLS, SMK, may increase the negative charges of clay particles, causing shale dispersion and Liborehole destabirty. In order to solve these problems, some cationic additives are used to decrease the negative charges of particles, therefore to increase shale inhibition and borehole stability. It was reported that cationic additives, such as cationic polymer, Amphoteric polymer and mixed metal hydroxide compounds (MMH), have been developed, and field evaluations all confirm superior benefits although the mechanism dealing with clay inhibition is different from each other. Since 1986, we have been studying the application of posItive sols in drilling fluids, a series of PS products, available for drilling fluids, have been developed, introducing a new kind of drilling fluids, i.e. PSDF. PS can be prepared from metal oxides, metal hydroxides, mixed metal oxides and mixed metal hydroxides, which has high colloid stability and zetal potential high up to + 30 + 60mV. In drilling fluids, positively charged particles can associate with negatively charged clay particles, forming stable gel structure. Simultaneously, PS can also decrease the negative charges of clay particles, forming weak negative system or positive system, which is beneficial to borehole stability. In another word, PS can stabilize the drilling fluid itself and borehole simultaneously. P. 569