Research On Horizontal Drilling Fluid Technology For Protecting Reservoir In Jilin Miaotaizi Block

The drawdown pressure of horizontal well is small, and the drainage area is big. So the horizontal well can control the water percentage's ascending velocity, increase the liquid producing capacity, and it has became an important technology in exploiting the new oil field and the old oil field to enhance the oil recovery. The horizontal well is used more and more in exploiting the low permeability oil field. In comparison with straight well, the drilling time of horizontal well is longer, and the drilling pressure is bigger, so the degree of drilling fluid's damage to the reservoir is severer than straight well. So, analyzing the recovery's damage mechanism and perfecting the using drilling fluid systerm are becoming more and more important.The type and quantity of clay mineral are analyzed according to the characteristic of Miaotaizi block. Building on the analysis of clay mineral, the sensitivity experiment is conducted. The sensitivity of Miaotaizi block are as follows: alkali sensitivity (midium), rate sensitivity (medium to low), water sensitivity (medium to low), salt sensitivity (medium to low in the decreasing salt sensitivity experiment; low in the increasing salt sensitivity experiment).The elements which affect the horizontal well's deliverability are analysed comprehensively. And the affecting degree of these elements for the horizontal well's deliverability of Miaotaizi block is also analysed. The result is that the formation damage is the most important affecting element in this block.Based on the analysis of the sensitivity and the affecting elements of the horizontal well's deliverability, The formation damage mechanisms is researched in the paper, the main reason of leading to the formation damage is adventitious fluid invasion, it means the main damage way is liquid phase damage. The solid phase damage is little. The computational methods of the drilling fluid's invasion depth are summed up systemicly, from the computational methods we can see that for the particular formation, the influence factors of the drilling fluid's invasion depth are filter loss, time and drilling pressure, this point can also be verified from the flollowing experiments.According to the distinguishing feature of Miaocaizi block, the temporary blocking agent which is suitable for the Miaocaizi block is manufactured, and the existing drilling fluid is optimized, the performance and the the reservoir protected effect of the optimized drilling fluid are very well.