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Automatic pH Controller (ApHC) for Oil Well Acidic Return Following a Stimulation (Acidizing) Job

IP.com Disclosure Number: IPCOM000200492D
Publication Date: 2010-Oct-15
Document File: 6 page(s) / 302K

Publishing Venue

The IP.com Prior Art Database

Abstract

Mathematical modeling is a useful and powerful approach to automation. Before development, it helps to evaluate the controllability and stability of the system as well as the sensitivity to parameters and external disturbances. Proper compensator, control board and program routines can then be designed for a robust control system. Such an approach was used to develop a process to control pH in an oilfield flow line known as an automatic pH controller (ApHC).

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Page 01 of 6

Automatic pH Controller (ApHC) for Oil Well Acidic Return Following a Stimulation (Acidizing) Job

Abstract

Automatic controlled mechanisms are one of the most fundamental processes in nature. They can be found in the human body, animals, plants, machines, economic systems, ecosystems and society. However, automatic system concepts have been used primarily by the engineering sector even though they are also used in other specialties. Theories and principals of an automatic system can be directly applied when designing a mechanism functions to regulate without routine intervention.

The first step when designing an automated system is to build a mathematical model by collecting the rules or mathematical equations that govern the phenomena. From the mathematical equations, one may define the parameters that are involved in control. Some of the parameters can be measured by gauges and others may be calculated.

Mathematical modeling is a useful and powerful approach to automation. Before development, it helps to evaluate the controllability and stability of the system as well as the sensitivity to parameters and external disturbances. Proper compensator, control board and program routines can then be designed for a robust control system. Such an approach was used to develop a process to control pH in an oilfield flow line known as an automatic pH controller (ApHC).

Introduction

The ApHC is a standalone system designed to automatically neutralize or adjust the pH of flow back returns following an oil well stimulation or acidizing job.
The ApHC saves rig time and allows flow back from the well through existing flow lines without the risk for the acid to damage production components.

When using the ApHC,
neutralization is achieved by
automatically injecting a basic
(alkaline) solution of caustic
soda (or other basic solution)
into the return line, which raises
the pH of the flow back fluid to an acceptable or desired level, usually up to between 4 and 7.

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Figure 1. Self-Elevation Workover Platform (SEWOP)

 


Page 02 of 6

The need for such a system came out when a client, in 2002, expressed his willingness to eliminate the rig/support vessel standby time and cost when waiting for the well to complete its acid flow back, which can take several hours, even days. A self elevation workover platform (SEWOP, see Figure 1) type rig was used and the daily cost was about $55K. Flow back average times were between 12 to 48 hours.

Description

The system, represented in the Figure 2, is composed of a choke to control the flow back (return) rate, a flow meter to measure that rate, a first pH sensor to measure the pH (acidity) of the flow back fluid before the neutralization point, and a second pH sensor to measure the acidity after the neutralized point. The system computes the required injection flow rate of the basic (alkaline) solution using a unique mathematical equation (AB junction equation) an...