Drilling Fluid Technology for the Third Interval of Sunan 23-113H2 Well

. In the construction process of Sunan 23-113H2 well, there wasYanchang well, Liujiagou well and Shihezi well, when passing through the well, the mudstone collapse of the large slope section caused the difficulty of reaming off, after repeated reaming off, the wellbore still cannot be unblocked. Finally, the well structure was changed from the conventional Third Interval to the optimized Third Interval, and the technical casing is lowered to the depth of the inclined 45° well in the inclined shaft section. After the Third Interval, the mudstone of the large inclined section and the horizontal section collapsed, and the well leakage of the inclined well section and the horizontal section was still prominent. According to the construction situation of the Third Interval of the well, this paper optimizes the drilling fluid and refines the leak prevention and plugging measures through indoor experiments to provide technical support for safe drilling.


Introduction
In First Interval and Second Interval, there were well leakage phenomenon in Sunan 23-113H2 well, and the risk of mud and rock collapse and leakage is high, which cannot solve the stability problem of the well wall, and the collapse contradiction is prominent [1][2][3].After the Third Interval, it still faces the collapse of mudstone and horizontal section, the collapse of the inclined well section and the horizontal section, and the contradiction between collapse and leakage is still prominent.According to the construction of Sunan 23-113H2 well, the best treatment agents were determined by screening the field treatment agents and classifying them according to their efficacy [4][5][6].Different drilling fluid formulations were designed to test the different formula density, API water loss, HTHP-FL(Filter loss under high temperature and high pressure), apparent viscosity, plastic viscosity, dynamic shear force, etc., to determine the best drilling fluid formulation, the system formula and plugging measures were optimized, and to conduct field experiments to provide technical support for safe drilling [7][8][9][10].

Water loss performance test
When the drilling fluid circulates in the wellbore, with the increase of density, the liquid injection pressure will increase, if the quality of the mud cake is poor, the water loss is large, the filtrate pressed into the formation is gradually increasing, exacerbating the collapse of the debris formation prone to collapse, so while increasing the density of the drilling fluid, it is necessary to reduce the water loss, the medium pressure water loss control is less than 3.0 mL, and the high temperature and high pressure water loss is less than 12.0 mL [11,12]..494Through the above calculation, the displacement plays a decisive role in the size of the annular air pressure consumption, so when drilling normally, the annular air return speed can reach more than 1.2 m/s, and the displacement is 12-13 L/s.

Anti-spill and plugging measures
Circulating tank is always prepared with 35 m 3 sealing drilling fluid, formula: drilling fluid+ 10% fine plugging, immediately after the leakage is lost, immediately pumped into the plugging drilling fluid, all replace the water eyelet, drilled into the casing for squeezing or static plugging.When increasing the density, each 1 ton of barite mixed with 200 kg of leak plugging agent with drilling, 1 ton of plugging agent with drilling is added to each tank of supplementary pulp, and single seal and KSD-1 are selected for plugging agent with drilling [13][14][15].

Solid phase control requirements
All drilling fluids were sieved, and the vibrating sieve screen cloth is selected at more than 180 meshes.Check the sediment volume of the conical tank per shift, reach 1/2 and immediately clear the tank.After 3-4 hours of use of the high-speed centrifuge, it is necessary to remove harmful solid phases such as inferior soil in the system.When preparing the supplemental drilling fluid, glue + KCL is mainly used for system maintenance, less barite is consumed, and the supplementary drilling fluid density is adjusted according to the system density [16][17][18].

Conclusions and suggestions
The drilling fluid formula was determined as: water +0.15% +0.1%XCD + 1%NAT-20+1% PAC-LV +2%NFA-25(2%SMP-2) +3%FT-401 +2%ZDS +15%KCl + 2%Pre-hydrated drilling fluid.The KCl content of large slope well section reacheed 15%, and the system had strong inhibition and can effectively prevent mudstone collapse.The drilling fluid improved the system pluggability, reduced water loss, and can effectively reduce the collapse pressure of the formation, which can reduce the density of drilling fluid and reduce the risk of well leakage.It is very important to reasonably select the displacement of small wellbore.On the premise of meeting the requirements of sand carrying, the displacement should be reduced as far as possible, which can greatly reduce the annular circulation pressure consumption and prevent the leakage of horizontal section Wells.When adjusting the performance of the system, it is necessary to carry out small experiments first to avoid blind operation and causing performance adjustments to be in place for a long time, causing downhole complexity.

4. 3
The third drilling process occurred two leakage in the drilling process, one squeeze and seal, one time with the drilling, only the drill pipe is drilled to plug the leak without drilling..

3 4. 4
After the Third Interval session, monitored the solid phase content every day, opened the centrifuge to clear the solid phase in time according to the solid phase content, and cleaned up the conical tank for each drill.

Fig. 2 4 . 5
Fig.2 Frictional resistance created by upward movement and downward movement in the third drill of Sunan 23-113H2 Well

Table . 2
Medium-pressure water loss value at different pressures

Table . 3
Liquid injection pressure at the same vertical depth and different density (vertical depth 3780m)

.3 Optimize the displacement and reduce the annular air pressure consumption Ring
-air pressure consumption was calculated at a well depth of 4000 m, a density of 1.35 g/cm3, and a plastic viscosity of 40 mPaꞏs.

Table . 4
Different displacement and annular return speed

Table . 5
Different effects of drilling plugging agent on the performance of drilling fluid

Table . 6
Performance of Third Interval drilling fluid in Sunan 23-113H2 well

Table . 7
The rheological energy of third drilling fluid in the Sunan 23-113H2 well at the same temperature

Table . 8
Statistics on the Third Interval leakage of Sunan 23-