Development and Evaluation of Various Drilling Fluids for Slim Hole Wells

Abstract

IntroductionDrilling cost optimization has always been, and will continue to be, the most important issue in the petroleum drilling industry. Using slim hole technology is one of the sure ways to achieve substantial cost savings. The basic difference between conventional wells and slim hole wells is the wellbore geometry. While the hole diameter of the production interval in a conventional well ranges from 6½ in to 9 5 /8 in, that of a slim hole well ranges from 3½ in to less than 6 in. Recent advances (1)(2)(3) in slim hole technology include the development of drilling fluids to reduce the APLs because 60% of the pressure loss occurs in the annulus of slim hole wells (1) .Some developments in slim hole drilling fluids design have included the works of Downs et al. (2) They formulated formate brinebased fluid with xanthan gum as a viscosifier. Randolph et al. (3) developed a unique weighting agent for slim hole drilling. In general, low solids-fluids are used to prevent the plating out of solids inside the drill string, and the fluids should have low viscosity to avoid an excessively large equivalent circulating density (ECD). These systems are very costly, thereby reducing the cost savings significantly. The purpose of this study was to develop a low-cost, low viscosity fluid that will reduce the annular pressure loss significantly while maintaining a gauged hole. Study MethodologyThis study involved the development of several fluids and their rheological characterizations with Bingham Plastic and Power Law models. The data were used for calculating APL gradients for three slim hole geometries and carrying capacities of the fluids. The fluids developed were water-based because they are cheap, environmentally accepted and they require little effort when detecting gas kicks. Two main groups of fluids were tested: bentonite (clay)-based fluids and viscosified brines. Salts were added to the fluids for wellbore stability. The two types of salts used in this study are potassium chloride (KCl) and potassium formate (KF). Xanthan and PHPA (partially hydrolyzed polyacrylamide) polymer were used as viscosifiers in the brines in order to investigate their effects on annular pressure losses. In all fifty-three (53) study samples, different fluids were formulated under atmospheric conditions and at 150°F. Tables 1 and 2 show the compositions and rheological parameters of selected fluids tested under atmospheric conditions and at high temperature.Thirty fluids exhibited Power Law behaviour while the remaining 23 exhibited Bingham Plastic behaviour. All brines with PHPA seemed to exhibit Bingham Plastic behaviour, while all brines with xanthan exhibited Power Law behaviour. The APL gradients were calculated using the rheological data from the two models. Table 3 lists the equations for estimating APL in the annulus for the two models. The pressure calculations were performed for flow rates of 22.2 gpm, 34.6 gpm and 100 gpm, and three wellbore geometries. The carrying capacities of the fluids were evaluated using the slip ...

Novel Equation for the Prediction of Rheological Parameters of Drilling Fluids in an Annulus

“…(d) T Type Data. The data of Enilari, 21 for water-based drilling fluids containing KCl and KF salts and xanthan, was also used. The data T1, T4, T10, T41, T42, and T43 have been reproduced in Table B1, Appendix B.…”

“…Two annulus geometries are used: (a) an annulus with an internal diameter equal to the outer pipe diameter of 0.311 m and an external diameter equal to the inner pipe diameter of 0.127 m and (b) an annulus with an internal diameter equal to the outer pipe diameter of 0.216 m and an external diameter equal to the inner pipediameter of 0.089 m. As it can be realized, the ratio of R 1 /R 2 > 0.3 is valid for both cases. According to the Enilari statement 21 for the cases that the above criterion is hold, the approximation of a slot for annulus geometry is a valid approximation. Results have been derived for a range of flow rates encountered in oil-well drilling situations, while keeping the flow regime laminar; which is the normal condition encountered in drilling applications, particularly for flow in an annulus.…”

“…In this research since the criterion of R 1 /R 2 > 0.3 holds, the annulus geometry was approximated as a slot. 21 Integration of the force balance in a slot for the flow performed on a fluid element gives the following: 14,22 τ ) τ 0 + y(DP) (C.1) Step 1: Determination of the rheological parameters for sample S19 using eq 6 or existing data from Table 3.…”

Application of soft computing approaches for modeling annular pressure loss of slim-hole wells in one of Iranian central oil fields

“…inch; yet this value may range from 3 1/2 to 6 inch in a slim-hole (Jafarifar et al, 2020;Azari and Soliman, 1997;Enilari et al, 2006). The pressure losses are significantly affected by the reduced annular clearance in slim-holes, while 90% of the pressure losses take place in the bit nozzles and the drill string in a conventional well.…”

Rheology and Flow Characteristics of Xanthan in Calcium Chloride Brine

“…In extended reach and slim-hole drilling, various types of salt have been added to clay-free water-based polymer drilling fluids to impart the necessary weight needed to overcome the prevailing formation pressure, wherein the polymer is expected to provide the viscosity needed to enhance the solid carrying capability of the fluids (Downs, 1991 and1992;Enilari et al, 2009). Viscosified brine drilling fluids have been engineered to reduce frictional pressure losses and ECD in slim-hole drilling, as well as improve temperature stability of the polymer (Howard, 1995).…”