Abstract
In the Missan oilfield, because of its reservoir being easy leakage in the up and low zones, and wellbore being collapse in the middle zone with narrow density window, borehole instability, lost circulation, borehole collapse, sticking and other downhole complicated conditions were easily induced. A strong sealing and high performance water-based drilling fluid was mainly used to solve the problems of borehole instabilities in mud shale and muddy limestone in the horizontal wells of Missan Oilfield, for solving the problem of sidewall instability, aphysical/chemical plugging was used for strengthening the plugging of drilling fluid, improving the loading ability in formation, reducing the risk of lost circulation. The principle of regulation, permeable pressure were used to improve the semi-permeable membrane characteristics of mudstone and shale, reduce the activity of drilling fluid, inhibit the expansion ability of mudstone hydration and expansion in formation, on the basis of the static drilling fluid, permeable pressure was added to the wellbore for further improvement of borehole stability. The system in use reflects the stable rheological properties, it can be very good for plugging micro fractures, greatly improving the load ability in formation, the delaying time of borehole stability, guaranteeing the borehole stability in drilling, it provides support for the smooth drilling of the first horizontal well and consequent horizontal well drilling in Missan Oilfield.
Highlights
IntroductionIn in Iraq's Missan Oilfield, due to the complexity of limestone leakage and shale collapse in the reservoir section, the horizontal well operation in this block is unprecedented
The main problem faced by drilling fluid for horizontal wells in Missan Oilfield is how to solve the problems of wellbore stability and leakage. the trend and characteristics of wellbore stability research are mainly unstable problems caused by geological factors, the interaction between shale and drilling fluid, drilling operations and other factors, i.e. wellbore stability, which is a very complicated worldwide problem encountered in drilling system engineering
3) Leakage prevention work in MISHRIF horizon: landing in mishrif horizon, with high density in the hole bottom, limestone fractures are prone to leakage. in case of irreversible leakage, it is bound to affect the smooth landing of the project, and the lowering of drilling fluid column pressure may cause the collapse of upper TANUMA horizon
Summary
In in Iraq's Missan Oilfield, due to the complexity of limestone leakage and shale collapse in the reservoir section, the horizontal well operation in this block is unprecedented. The main problem faced by drilling fluid for horizontal wells in Missan Oilfield is how to solve the problems of wellbore stability and leakage. Lei Zhiyong et al.: Application of Strong Sealing High-performance Water-based Drilling Fluid in the Horizontal Well of the Missan Oilfield of magnitude faster than solute and ion diffusion, and solute and ion diffusion is 1~2 orders of magnitude faster than drilling fluid filtrate; the stabilization of borehole wall must be carried out simultaneously with the control of pressure infiltration to be effective. The author chose a strong plugging high-performance water-based drilling fluid system, which greatly improved the pressure bearing capacity of the borehole wall, avoided the risk of leakage, and increased the formation pressure bearing capacity by 0.15g/cm[3]. Sandstone and Black Brown Shale Interbedded Clay bright white limestone Pore-developed limestone Clay bright white limestone Top: malr; middle: thin limestone; lower: longer shale White limestone Pore-developed limestone and dense limestone
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