Surge and Swab Pressures in Horizontal and Inclined Wells

Abstract

Surge and swab pressures generated during well construction operations are critical. As thousands of wells are drilled every year, challenges associated with downhole pressure management have become more important for the oil industry. Inadequate estimation of surge and swab pressures can lead to a number of costly drilling problems such as lost circulation due to formation fracture, fluid influx resulting in kicks, breakdown of the formation at shoe due to limited kick tolerance or blowouts. An accurate surge pressure model is very important in planning drilling operations, mainly in wells with narrow safe pressure window, slimholes, low-clearance casings, deepwater, and extended-reach well applications.Existing surge/swab pressure models assume concentric wellbore. This assumption is hardly ever valid in horizontal and inclined wells with some degree of eccentricity. Ignoring the pressure reducing effect of eccentricity on surge and swab pressures may eventually lead to underestimating the tripping speeds, and thereby increase non-productive time and operation costs. Eccentricity between the wellbore and the drillpipe adds more complexity to surge and swab pressure calculations. Recent studies have indicated that surge pressure can be significantly reduced due to eccentricity. Although the numerical investigation shows encouraging results, understanding of pressure surges in wells with eccentric annular geometry is very limited.This paper presents the results of experimental investigations conducted to study the effects of eccentricity on surge and swab pressures. Experiments were performed in a test setup, which consists of fully transparent polycarbonate tubing, and inner pipe that moves axially using a speed controlled hoisting system. During the experiments, test fluid viscosity, trip speed, and eccentricity were varied. Experimental results were compared with predictions of existing models showing a satisfactory agreement. Results confirm that trip speed, fluid rheological properties, annular clearance and eccentricity significantly affect the surge pressure. In some cases, eccentricity can reduce surge and swab pressure by around 40%. Applying regression analysis, a generalized correlation has been developed to account for the reduction in surge pressure due to the eccentricity of the drillpipe.

Modeling of Swab and Surge Pressures: A Survey

“…The main objective of this study by Srivastav et al [10] is to examine the effects of different drilling parameters such as trip speed, fluid rheology, and eccentricity on swab and surge pressures. The model is summarized in Equations ( 53) to (67).…”

“…The following assumptions were presumed during the model formulation: Since the whole point of the models was to do experimental studies, the authors [10] used an existing small-scale setup. The setup is explained in detail, and the figures compare the experimental results with their models' predictions.…”

“…( 7), ( 8), ( 14), ( 18), (21) t Y Mud yield point in lbs./100 sq.ft. ( 7), (10) n Plastic viscosity of the mud in Centipoise. ( 7), ( 18), (…”

“…Equation ( 10) is used for computing the lower critical velocity value (based on R = 2000 in Laminar Flow) at which the flow changes from laminar to turbulent. Equations ( 7) to (10) can be implemented to calculate the bottom hole pressure provided the equivalent velocity formed of served displacement and clinging velocity. For different conditions, the equivalent velocity can be calculated from Equations ( 11)- (13).…”

Study on the Surge-Swab Pressure considering the Effect of the Cutting Plug in Shale Drilling

“…Cannon [11] conducted tests to measure pressure changes with downhole pressure gauges when withdrawing pipes, regarding that the pipe withdrawing entails wellbore pressure reduction and might lead to blow-out accidents. Later, more experiments were conducted, and field data was investigated about surge-swab pressures [12][13][14][15][16], mostly for validation and improvement of theoretical models. Besides experimental work, theoretical studies are dedicated to establishing models of the surge-swab pressure, including steady-state models and dynamic (or transient) models.…”