Pressure relief process for well-drilling

• US 4,852,667 A
• Filed: 06/26/1987
• Issued: 08/01/1989
• Est. Priority Date: 07/02/1986
• Status: Expired due to Fees

• Current Assignee: Total Compagnie Francaise Des Petroles
• Original Assignee: Total Compagnie Francaise Des Petroles
• Inventors: Dorleans, Andre M.
• Primary Examiner(s): Kisliuk, Bruce M.
• Application Number:
  US07/066,599
• Time in Patent Office: 767 Days
• Field of Search: 175/215, 175/65, 175/213, 175/100, 175/339, 175/340, 175/393, 175/324
• US Class Current: 175/65
• CPC Class Codes: E21B 17/1078 Stabilisers or centralisers for casing, tubing or drill pipes devices for off-center positioning E21B17/10; E21B17/1007 - E21B17/1064 take precedence
• CPC Class Codes: E21B 21/08 Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure valve arrangements therefor E21B21/10
• CPC Class Codes: E21B 41/0078 Nozzles used in boreholes drilling by liquid or gas jets E21B7/18; drill bits with nozzles E21B10/60; perforators using direct fluid action E21B43/114; obtaining a slurry of minerals using nozzles E21B43/29

Abstract

A drill string has a bulge equipped with a system of n injection ducts connecting the interior of the string surrounding annular space and opening upwardly into the space to divert a part of the drilling fluid supplied to the bit. This arrangement makes it possible to produce below the bulge a pressure decrease H markedly greater than 10 meters of water by setting the flow of drilling fluid in the system of injection ducts at a value, expressed in m³ /s, equal to approximately: √10H×S×s33 n, S and s being the cross-sections, expressed in m², respectively, of a part of the portion of the annular space included between the periphery of the bulge and the drill string and of the group of n injection ducts.

Claims

1. A well drilling process using a drill string (3) carrying a dril bit (2) at a lower end thereof and comprising, above the drill bit, an enlargement (4) having a maximum external diameter smaller than the diameter of a bore hole being drilled and provided with a system of n injection ducts (6) connecting an interior (7) of said drill string to an annular space (8) between the well and said drill string and opening upwardly into said annular space, comprising the steps of:

(a) pumping drilling fluid downwardly through the interior of said drill string,

(b) diverting a portion of said drilling fluid into said annular space via said injection ducts, the remainder of said drilling fluid flowing downwardly to said drill bit from where it passes upwardly around an exterior of said enlargement and into said annular space, and

(c) selecting the flow Q of said diverted portion of drilling fluid, expressed in m³ /s, to provide a difference H, expressed in meters of head of water, in the pressure of the drilling fluid below said enlargement relative to the pressure of said drilling fluid at a level of said enlargement in the absence of said injection ducts, greater than a threshold value of H=10 m, and substantially in accordance with the equation;

space="preserve" listing-type="equation">Q=√

10H×

S×

s×

n,

wherein s and S are respective cross-sections, expressed in m², of an annular space above the enlargement between an imaginary cylinder extending an outer periphery of the enlargement upwardly and the drill string, and of the injection ducts, and 10 is an approximate value of gravitational acceleration in m/s².

2. A process according to claim 1, wherein the well has a diameter D, and further comprising the step of selecting the maximum external diameter of said enlargement to be at least equal to 0.88D.