Research and application of soft-inhibitive drilling fluid system in Chenghai 1-1 block of Bohai Bay
The Chenghai 1-1 block in Bohai Bay is developed using cluster wells.During the second spudding operation,a pure sylvite polymer drilling fluid system is widely used.The lattice substitution effect of potassium ions can lead to the formation of a hard shell on the wellbore wall,but the internal shale will continue to hydrate and expand,causing difficulties in tripping in and out and even resulting in complex downhole conditions such as the failure to lower the technical casing to the proper position.In response to this situation,the small molecule cation inhibitor BDSC-100L was introduced into the traditional pure KCl polymer drilling fluid system to improve the ability of the drilling fluid to inhibit the hydration and dispersion of clay.At the same time,the low-concentration KCl and high-concentration NaCl were combined to improve the ability of the drilling fluid to inhibit the hydration and expansion of clay.Based on this,a soft-inhibitive sylvite polymer drilling fluid system was developed.Laboratory tests show that the recovery of rock cuttings from soft-inhibitive sylvite polymer drilling fluid is twice that of pure sylvite polymer drilling fluid,and the shape of rock cuttings remains intact after hot rolling.Field applications indicate that soft-inhibitive sylvite polymer drilling fluid is superior to pure sylvite polymer drilling fluid in terms of wellbore stability and wellbore cleaning.
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