Maximum allowable pressure during heavy slurry displacement
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ORIGINAL PAPER-PRODUCTION ENGINEERING
Maximum allowable pressure during heavy slurry displacement Abdeslem Leksir1 Received: 30 March 2020 / Accepted: 13 July 2020 © The Author(s) 2020
Abstract Heavy slurry pumping is facing enormous problems concerning pressure generation and casing limitations. Pumping highdensity cement throughout narrow column, throttled at their extremity by the float equipment will generate more pressure, and could push casing to their limits of utilization. There are numbers of phenomena that could lead to casing length change as: piston, ballooning, temperature, tension and buckling. This work is oriented to study buckling effect on total casing length change. Generally, in conventional wells cementing, down hole conditions are referred to geological formation fracture pressure limit, which is lower than buckling limit. Heavy slurry displacement could make an exception, where buckling could appears at pressure inferior to geological fracture limit. While pumping heavy cement down, pressure inside casing increases progressively, pushing casing to extend, consequently risk of closing the narrow space out between casing and open hole total depth may appears. At this moment, buckling begins; pressure rise intensely to reach geological fracture limits and causes down hole loses. After passing the critical high pressure situation, casing will come back to their initial form. In order to overcome this situation, maximum allowable pressure during displacement together with problem indicators is proposed, to prevent and early detect the problem. Experimental and simulation results confirm the usability of assumption proposed. Keywords Heavy cement job · Casing limitations · Maximum allowable surface pressure · Buckling indicators List of symbols Fb Buckling force (fictitious force) (lbf) Fa , T Tension force of casing string (lbf) Fad Additional buckling force caused by change in pressure from internal to external casing (lbf) Fc Critical buckling force, lbf Ai Area of the casing internal diameter, (in2) Ao Area of the casing outer diameter, (in2) BBof Buoyancy force (lbf) Bf Buckling force engender by buoyancy force (lbf) E Elongation due to tensile load (in) ΔE Variation elongation due to change in tensile load (in) Pi Equivalent inside casing bottom pressure, (psi) Po Equivalent annulus bottom pressure, (psi) N Neutral point, in W The buoyed weight per unit length, lbf/in Ws Weight of steel per unit length, lbf/in Wi Weight of fluid inside casing per unit length, lbf/in
* Abdeslem Leksir [email protected] 1
SONATRACH, University of ANNABA, Annaba, Algeria
Wo Weight of fluid outside casing per unit length, lbf/ in Pihyd Equivalent inside casing hydrostatic pressure, (psi) Psurf Surface pressure, (psi) Pmax Maximum allowable Surface pressure, (psi) PΔL Trapped pressure due to buckling effect
Introduction Cementing job is one of the most critical operation executed during well life cycle, represents long production period or safe abandonment, this is according to how
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