Abstract

Horizontal wellbore drilling technology has drastically escalated the productivity of oil and gas and become a portentous technology in petroleum industry. However, horizontal wellbore drilling is principally hampered by wellbore cleaning hydrodynamics which in turn is complicated by the buildup of drill cullings in the lower side of the annulus thereby reducing the drilling rate and transport performance of drilling fluids. A method and apparatus has been developed to enhance wellbore cleaning employing a transverse axial-travelling dynamic-pressure jets system (TAD-Jets system) in collaboration with conventional axial laminar flow in a multiple variant conduits, orbically cascaded and embedded in the drillstring. In tandem, a single twenty-seven-variable equation has been derived which has the capability and versatility of predicting the transportation efficiency regardless of the wellbore geometrical architecture, formation heterogeneity and rheological properties of the drilling fluid there-in annulus confined. Practical examples are presented to test this mathematical model.

Introduction

The concept of horizontal wellbore cleaning pertains to heterogeneous flow of complex mixtures of solids in horizontal pipes.1,2 Many investigators have attempted to solve the problem of horizontal wellbore cleaning through three main avenues: Designing drilling fluids systems of various physico-chemical compositions with the hope of increasing fluid carrying capacity.3,4,5 Designing drilling pipes with ridged external geometrical configurations capable of conveying drillcuttings utilizing auger principle as well as optimizing drillstring rotational and reciprocational motions to induce drillcuttings dynamic suspension and increase drilling fluid carrying capacity6,7; The third approach has been to optimize drilling fluid velocity profile by manipulating the regime a f flow between laminar and turbulent8,9,10.This has resulted into many drillcuttings transportation model like Moore's, Chien's, Zedlers' and Iyoho's just to mention a few. Although these research works have contributed significantly to the solution of this problem, nonetheless wellbore cleaning problem has yet to be understood and solved because up to now wellbores collapse when the turbulent flow meant to enhance carrying capacity of the drilling fluid exceeds formation fracturing pressure. On the other hand drillstrings do stick in the wellbore when tfe drilling fluid flow is too low to dislodge, dynamically suspend and convey the drillcuttings from the annulus below the dril1string. In the current study an attempt has been made to design a transverse axial-travelling dynamic-pressure jet system which will enhance the dynamic suspension of drillcuttings and improve their- transportation in a laminar flow regime. The overall aim is to enhance transportation efficiency of any given drilling fluid without: increasing the conventional flow rate above its critical value, increasing drillstring motion and changing drillstrings external geometrical configuration. This approach will be most appropriate for turbodrilling where the drillstring does not rotate and it's reciprocational motion is minimum. The system will reduce the necessity of manufacturing different drilling fluids which could pollute environment. Wellbore stability will be improved as drillpipe motion is not needed for the systems operation. This will ensure safe drilling and reduced drilling time and cost.

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