Well-Control Analyses on Extended-Reach and Multilateral Trajectories

Abstract

For economic and technical reasons, the industry has used directional, extended-reach, horizontal, and multilateral wells. Although technologies are well developed for these wells and there are numerous successes in the last decade, these wells still have high levels of risk in drilling and completion. Well control is one of the relatively unanswered but important operations, because improper well control, followed by a blowout, is one of the most expensive and feared operational hazards.To maintain a specified bottomhole pressure (BHP), surface choke pressures highly depend on kick vertical height in the well and well trajectory. As the final hold angle of the well increases from vertical, shut-in casing pressure (SICP) reduces to shut-in drillpipe pressure (SIDPP) and remains the same as long as the kick stays in the horizontal section. For equal vertical depths, the maximum choke pressure is insensitive to hold angles or hold lengths, as long as the initial pit-volume gain is the same. However, for directional and extended-reach wells, choke pressure can increase even without kick expansion, because of the gain of kick vertical height in the build section. This may mask choke-pressure reduction because of larger annular capacity when the kick passes the casing shoe, especially if the kickoff point (KOP) and casingshoe depth are close.In multilateral wells with more than one kicking wellbore, SIDPP is affected by both formation overpressure and kick size in each wellbore. The maximum value among them will appear at the surface. Therefore, we should be careful in the interpretation of the shut-in pressures. For safe kick circulation, we must consider additional pressure to compensate for hydrostatic-pressure reduction resulting from kick migration and expansion in branch wellbores. Two-Phase Kick Model.The appropriate assumptions and governing equations are critical to simulate realistic well-control operations. There are two typical types of assumption for modeling a gas kick: one is two-phase, and the other is single-phase. Considering the kick as a two-phase mixture, there are many computer models 6-8 for analysis of transient kick behavior. Eight variables describe the two-phase flow system completely. They are pressure, temperature, gas and liquid fractions, gas and liquid densities, and gas and liquid velocities. For water-based muds, we typically assume there is incompressible mud with a known temperature profile in the wellbore. Therefore, there are five unknowns: gas

Well Control Simulation Model of Oil-Based Muds for HPHT Wells

“…Choe and Juvkam-Wold (1997) presented a modified two-phase well-control model. This model was applied in horizontal and extended-reach wells and gave reliable results without numerical problems (Choe et al 2005). Rommetveit et al (1989) studied well-control with OBM considering gas solubility and fluid density changes.…”

Modeling the Energy-Saving Regimes of Curvilinear Bore-Hole Drivage

“…Inasmuch as the inclined and hori zontal bore-holes penetrate the oil-and gas-bearing strata along the laminated structure of the underground deposits, they cover larger zones of fuel output and are effective expedients to enlarge the extraction efficiency [1][2][3][4]. Inasmuch as the inclined and hori zontal bore-holes penetrate the oil-and gas-bearing strata along the laminated structure of the underground deposits, they cover larger zones of fuel output and are effective expedients to enlarge the extraction efficiency [1][2][3][4].…”

Hydraulics and Well Control Complications in Unconventional Shale Laterals

“…Waiting for mud preparation escalates the chance of gas migration and pressurizing the wellbore (Grace, 2003). Moreover, the step-down chart calculations in deviated wells are complicated (Santos, 1991b;Choe et al, 2005). Although, in vertical wells, Wait-and-Weight method decreases wellbore pressures, in horizontal wells Driller's method is applied to avoid delay time.…”

“…Hence, a vertical well step-down is invalid for horizontal wells (Santos, 1991a). In multilateral trajectories, step-down charts are complex and need to be computer generated (Choe et al, 2005). Driller's and W&W methods assume the gas invades the wellbore as a continuous slug and remains at the bottomhole with no migration.…”

“…The advantages of the Driller's method are the simple calculations and the lack of waiting time due to mud preparations. Additionally, it can control swabbed gases without the need to increase mud weight (Choe et al, 2005). The drawbacks are longer circulation time, and higher pressures in the annulus and at the casing shoe with the risk of fracturing the formation.…”