An Advanced Solution: The Drilling Adviser
Authors: Courteille J.M. , Fabre M. , Hollander C.R. 
Published: December 2007

This paper discusses the Drilling Advisor, a computer-based consultant whose goal is to provide advice about the cause and possible treatments of problems encountered during the drilling of wells. With the "Expert Systems" technique, a large amount of human knowledge can be represented as data structures in the system and efficiently used to make conclusions about the problem. Currently, the system handles sticking and dragging of the drillstring in the open hole.

Introduction

Artificial intelligence is the part of computer science concerned with designing intelligent computer systems. Recently, the field of Expert Systems, or "knowledge engineering, has emerged from this large research area and proved to be useful in some applications. (The MYCIN project-whose goal is to diagnose a bacterial infection project-whose goal is to diagnose a bacterial infection and recommend the best therapy-is one of these. ) Typically, Expert Systems can be viewed as intermediaries between human experts-who interact with the system in a "knowledge-acquisition" mode (adding new knowledge into the system, usually in the form of "if/then" rules)-and human users-who interact in a "consultation" mode. Furthermore. these systems have the capacity to explain their reasoning, which makes the consultation more acceptable and helps the human expert find errors or missing knowledge. Drilling is a domain for which experience is very important. Until now it was quite impossible to acquire this kind of knowledge from field experts and make it available for use by new engineers. Expert Systems addresses this difficulty directly, allowing expertise to be represented within the system and thereby making it usable on drilling sites to help solve problems. The system assists the driller and helps him make decisions in all kinds of situations, which leads to more efficient drilling and to saving money by saving time. Having the experience and the rules of art encoded in a machine can also be very useful for training purposes. The conservation and communication of the know-how and experience accumulated by our technicians as a result of their daily operations is already a permanent objective. and here knowledge is a key resource. For all these reasons, Soc. Natl. Elf Aquitaine and Teknowledge Inc. have jointly undertaken to build an expert system, first called the Drilling Advisor, then SECOFOR. The system currently handles both dragging and sticking incidents, but most of the knowledge already entered in the system could be used to handle other types of incidents as well. For each problem submitted, SECOFOR provides two types of advice:a diagnosis indicating the most likely cause(s) of the problem with a set of reasons supporting its conclusions, anda set of treatment recommendations aimed at solving the current problem and preventing its recurrence. preventing its recurrence.

Problem Definition Problem Definition We will not explain how a drillstring gets stuck. We will consider only those problems that happen in the open hole-between the casing shoe and the total depth (TD)- as a result of some undesirable interaction between the geological formations, the drillstring, and the drilling mud. The diagnosis phase of a SECOFOR consultation gathers evidence and tries to classify the problems as one or more of three main causes of sticking or dragging.

Differential Pressure. In conditions of differential pressure (DP), the mud's specific gravity exceeds the pressure (DP), the mud's specific gravity exceeds the equivalent gravity of the fluids in some permeable formation of the open hole. The sticking may occur if some smooth element of the bottomhole assembly (BHA) or the drillpipe comes into motionless contact with the cake left by the mud on the sidewall. The pressure gradient inside the cake generates a strong "sticking force," even for thin cakes. This is the most frequent cause of all sticking cases.

Annulus Plug. This cause of sticking is a direct result of some characteristics of the formations in the open hole. it has been subdivided into three individual causes, all of which result in the annular space being completely plugged by materials from the formation.

Sloughing. Sloughing is the result of sidewall material falling into the well (e.g., foliated shales or disaggregated rock break up when the mud and the hydraulic parameters are inadequate). parameters are inadequate). Balling Up. Balling up happens when the cleaning effect of mud circulation on the annulus is unsatisfactory (e.g., bad viscosity, low flow rate, and gumbos). Tight Hole. Tight hole is caused by creeping or swelling formations closing in on the drillstring, thus trapping it (e.g., salt).

JPT

p. 899