Petroleum related well drilling is now usually attended with the necessity to determine the location of the drill bit relative to the surface location of the well site. In most cases economic considerations, or government regulations, make it necessary to control the course of the drill bit throughout the deeper portion of the drilling process. The need for information and control has fostered the development of well bore communications. Communication is usually a matter of conveying data sensed down hole to receivers at the surface well site.
Most communication from a down hole location in a well is carried out by encoded, time spaced, pressure pulses in a fluid stream moving down the bore of a pipe string. The pulses are usually generated near a drill head operating in a well. In addition to drilling related data, such as angle off vertical, the pulser can communicate information related to various other conditions measured in a well.
In general, current MWD measurements are communicated by code carried by standing pressure waves in fluid pumped down hole in a pipe string or by time spaced digital pulses. In known cases the pressure variations travel from the down hole location to the surface where they are detected in the drilling fluid, or mud, circuit in surface gear.
Currently, MWD equipment used down hole interferes with directional control apparatus that tends to occupy some length of the drill string that is more effective if located near the drill bit. That, generally, forces the location of MWD farther from the drill bit. Data then transferred from sensors located in the MWD systems read data too far from the accomplished directional results.
Standing pressure waves are generated by apparatus often called a mud siren. The mud siren is a form of rotary valve apparatus, usually used to vary the resistance to a fluid stream moving down a pipe string. Digital pressure pulses may be created by a signal valve through which most of the fluid stream passes. This is called a positive pressure signal. Digital pulses can also be generated by by-passing some fluid from the pipe string to the well bore to reduce the resistance to fluid flow in the bottom hole assembly. These are called negative pressure pulses. The usual positive digital pressure pulses are of short duration and usually have a repetition rate of four pulses per second, or less. The negative pressure pulse generator is usually much smaller than the positive pressure pulse generator and the repetition rate could logically be higher than that achieved by the positive pressure pulse generator.
MWD packages can be of several forms. They can be installed in a drill string serial element or run into the bore of a drill string after it is in the well. Also, there are “hybrids” of the two systems such that batteries alone, batteries with instruments, or other combinations can be run into the drill string bore to join up with the parts mounted, or installed, in the drill string serial element. The installed system offers the ease of providing mud flow generated electric power down hole, but it must be very reliable to avoid costly round trips of the drill string to replace failed MWD assemblies. The most used arrangement today appears to be the shuttle MWD package that utilizes an orifice installed in the drill string. That situation suggests enduring problems with MWD systems in general.
If MWD systems become quite reliable, they will likely evolve to the installed version. The earlier systems were installed. The shuttle system, is somewhat troublesome itself, but it made more serious problems manageable.
MWD systems exist in either the positive pulse or negative pulse versions, but no shuttle packages are known that deliver negative pulses achieved by the process of by-passing mud through the drill string wall.
Evolution of MWD activities have proceeded in steps largely dealing with solutions to stubborn problems. Early successful mud pressure signal pulsers had little MWD support and served primarily as drilling turbine speed indicators, or tachometers. Such pulsers were powered by the turbine being monitored. When MWD systems were developed, a pulser was available but a substitute for the drilling turbine was needed. Operation of flow resisting signal valves down hole requires power. Down hole fluid powered motors, substitutes for drilling turbines, have been used to generate power to operate the signal valves, which were moved by fluid powered cylinders. This process brought considerable apparatus into the process, all of which was prone to result in operational uncertainties. Operational uncertainties are not very acceptable in expensive and dangerous well drilling operations.
The need to reduce the apparatus involved in generating digital pulses resulted in the development of self powering valves. My U.S. Pat. No. 3,065,416, issued Nov. 20, 1962 ushered in that self-powered era. These valves were powered by the pressure generated by the valve itself. These early self-powered valves had poppets that moved against the mud stream toward an orifice through which most of the mud stream flowed. The mud stream passed through the signal valves with high velocity. The high velocity mud impinged upon the apparatus and resulted in serious erosion problems. The self-powered signal valve required only a small servo valve and the need for power to manage the pulser was a minor problem. No solution to the erosion problem is known before 1992.
The erosion problem was reduced by turning the self-powered valve upside down. The Jeter, et al, U.S. Pat. No. 5,103,430, issued Apr. 7, 1992 led the extended use of the upside-down, self-powered, signal valve. The high velocity mud leaving the signal valve expends its energy in the general mud flow channel down stream of the signal valve. Below the signal valve, there is little or no related apparatus. Currently, the upside-down valve appears to dominate the MWD operations world wide. The upside down valve benefits from the fact that the velocity of fluid entering the orifice can be converted to stagnation pressure in the bore of the poppet situated upstream of the orifice to realize a pressure that is representative of the stagnation pressure downstream of the orifice.
As expressed herein, an open ended poppet situated upstream of an orifice, in the velocity field of the orifice, is defined as a source, or pressure tap, downstream of the orifice. That is anticipated by and is within the scope of the claims.
All self-powered, upside-down, signal valves now known still use a servo valve, often called a pre-valve, to control mud flow to a piston providing thrust to move the self-powered valve relative to the cooperating orifice. A mud flow restrictor combination that enables the servo-valve to control the signal valve greatly limits it's repetition rate. Further, efforts to bolster the repetition rate has resulted in utilization of the shortest practical stroke of the poppet. The short poppet stroke about prohibits the use of pulse amplitude controllers, which require more stroke of the poppet. There is a need to eliminate the servo valve.
There is serious need for some way to pass a communication conductor axially through the pulser. Elimination of the servo-valve may allow the bore of the poppet to be enlarged and to extend farther into the pulser. Enlargement of the bore of the poppet may enable the use of mud powered apparatus, such as electric power generators and hydraulic pumps, that need an open exhaust channel to the mud stream below the orifice.
There is a serious need for a conductor to pass through the pulser to allow sensors and controls to be placed near the drill bit. Currently, poppet control apparatus utilizes the generally central area of the pulser. If the poppet is made tubular, the ancillary features need also to be able to accept an axially extending tubular poppet.
A reliable MWD system, with a high probability of lasting a long bit run, and supplying the needed electric power, does not demand a shuttle system. It can be installed in the drill string as a serial element of the drill string to be changed out at the end of each bit run.