Combination of Spirolizers and Spring Centralizers Reduces the Risk of Differential Sticking: Case Study of Wells in Shell Petroleum Development Company (SPDC), Nigeria

Abstract

Over the past 4 years, there have been several stuck incidents during installation of liners and casing in some wells in Shell Petroleum Development Company (SPDC), Nigeria. In most cases, the sticking mechanism was identified to be differential due to high pressure over balance across some depleted sand intervals. Attempt to free the casing or liner string was successful in few of the cases, while in others, it resulted in either cementing the casing in place at the stuck depth and deploying contingency option where they exist or going through the long, rigorous and expensive process of fishing, plugging back and sidetracking. Investigations into these incidents pointed mostly to the casing centralization. During casing installation, a good standoff is required to keep the casing string away from the wall of the well bore to avoid differential sticking and achieve good cement placement. On the other hand, excessive centralization could lead to increased drag force particularly in deviated wells with the attendant risk of not getting the casing to bottom. Prior to casing installation, it is a standard practice to run simulation on centraliser spacing to achieve an acceptable standoff. Bow spring centralizers are commonly used especially for 9-5/8" casing installation and experience has shown that placement of these centralisers to achieve the acceptable standoff in order to avoid differential sticking as well as good cement distribution has led to having a casing string packed with centralisers thereby increasing the drag force. It therefore became imperative to develop a strategy for optimum centralizer placement in order to achieve both the acceptable standoff to avoid differential sticking and minimum drag. This paper discusses the approach taken to achieve this acceptable standoff with minimum drag force using a combination of Spirolizers and Bow spring centralisers and its impact in reducing the risk of differential sticking.

Numerical Computation Studies and Hydrodynamic Analysis on the Cutting-Carrying and Lifting Capacity of Spiral Centralizer in Gas Drilling

“…In the equation ( 1), the left first term is the change rate of turbulent kinetic energy; the second term is the convection transport of the time average movement; the right first term is diffusion transport; expresses the kinetic energy caused by velocity gradient, it can be got from the equation (3) to (5). (5) b G expresses the kinetic energy caused by buoyancy:…”

“…Now substantial studies in both theory and experiment about the migration mechanism of cutting in gas drilling have been conducted by scholars both at home and abroad [1][2][3][4] , produced a lot of important conclusions, however the report about the research on the theory of cutting-carrying ability of the spiral centralizer is rarely, only references [5][6][7][8][9] discussed its flow field and the structure in conventional drilling.…”