Fluid-Fluid Displacement for Primary Cementing in Deviated Washout Sections

Abstract

One of the most critical operations during well construction is the cementing procedure, where drilling fluid is displaced by cement, normally with one or more spacer fluids in between. Due to the curing nature of the cement slurry there will be only one opportunity to cement the well properly. Although one for top hole cases can fill cement in from the top in a remedial operation, this possibility cannot fully compensate for a non-optimal initial cement job. Furthermore, it cannot be applied to other well sections. In those sections, complex squeeze cementing operations may be necessary. Consequences of improper annular cement can be leakage during production phase and extensive costs when the well is to be plugged for abandonment after the production phase. To ensure that the risk of poor cement is minimised it is important to use the best procedures to place the cement properly. Most models in use assume that the annulus is homogeneous. This is not always the case since washout sections appear during drilling. The effects of these on cementing are not sufficiently studied and considered in models and procedures. Here we present and discuss results from fluid displacement experiments in a laboratory flow loop, illustrating annular displacement of drilling fluid by spacer (or spacer by cement). Model fluids with realistic densities and rheological properties have been used in a test setup with a transparent annular section. The wellbore is represented by a 10 m long test section, where the annulus has a 6,5” outer diameter and an inner string of 5” that can rotate. A washout section is represented by a 2 m long section of the outer pipe with a larger diameter of 11”. These diameters are representative for the lower parts of a well were high wellbore inclinations are common. In these sections the inner pipe cannot be assumed concentric at all times, so both concentric and eccentric positions have been tested. Experiments reported here were conducted at 60 degrees inclination. The test section was instrumented with conductivity probes in an array around the perimeter at 4 separate positions along the pipe, including the inlet and outlet of the washout section. Together with a camera along the test section, this provided information about the motion and shape of the liquid-liquid interface through the test section. Results show that the displacement front changes significantly when entering the washout zone compared to the regular annular section. Due to the larger flow area the density differences between displaced and displacing fluids become more important in the washout section, while momentum effects dominate in the regular section.

Primary cementing of horizontal wells. Displacement flows in eccentric horizontal annuli. Part 1. Experiments

“…Conductivity can give more local information, e.g. an azimuthal distribution of displacement efficiency as in Tehrani et al (1992), or by the use of multiple axial banks of probes as in Lund et al (2018) and Skadsem et al (2019). However, typically the number of probes remains limited and spatio-temporal features of the flow remain obscured, e.g.…”

Experimental Methods for Investigation of Drilling Fluid Displacement in Irregular Annuli

“…Finally, the suitability of the device that was applied in the displacement studies presented by Renteria et al [2], Tardy [4], Ytrehus et al [16], Lund et al [17,22] and Skadsem et al [18] has been verified. Note that some of these studies have been used in development of displacement software.…”

“…The experimental equipment presented here is designed for displacement measurements with non-hardening laboratory fluids, which is an applicable way of evaluating displacements experimentally [2,4,[16][17][18]. The two main approaches for monitoring the motion of the interface between the displaced and displacing fluids have been optical/visual and electrical resistance.…”

Experimental Study of the Use of Tracing Particles for Interface Tracking in Primary Cementing in an Eccentric Hele–Shaw Cell

“…These studies generally stated that turbulent displacement flow is more efficient than the laminar displacement flow [17,18], and the increasing standoff causes a significant effect on the displacement flow of the fluids and cement placement [20][21][22]. In cases like washout sections, the effect of inner pipe eccentricity is not significant for displacement in the washout section [23]. Moreover, inclination reduction is beneficial for the displacement efficiency within the hole enlargement for both concentric and eccentric annuli and in the regular part of the annulus in front of the enlargement [22].…”

“…By using large-scale eccentric annular geometry, the importance of the rheological properties of the realistic non-Newtonian fluids for fluid flow and hole cleaning performance was expressed extensively [14][15][16], and the propagation of the fluid interfaces and displacement efficiency were characterized [24]. It was indicated that an enlarged irregular section, i.e., a washout causes an improvement in displacement in some scenarios in strongly inclined wellbores [17]; while being independent of the displacement efficiency in the washout itself, the presence of washouts may lead to poorer cement quality downstream of the washouts [23].…”