The drilling technology was developed to increase the drilling efficiency based on 3 basic reasons, i.e.: safety, minimum cost, and usable hole. Casing drilling is one of drilling technology which it has been applied in many oil fields in Indonesia. The casing drilling is classified into 3 methods, i.e.: Retractable Bit, Liner Drilling, and Drilling with Casing, where each method can be applied in certain condition. Recently, the drilling technology has reached efficiency significantly, both in engineering and economical aspects, especially in the formation which is difficult to drill with conventional drilling method, for examples: Abnormal/subnormal zone Thief/loss zone Unstable formation Generally, the drilling efficiency can be formulated based on statistic trend from the field data. Thus, casing drilling can be developed to reach the drilling efficiency according to the field experiences.

DRILLING MODEL THEORY AND OPTIMAL DRILLING METHOD Meng Yingfeng, Southwestern Petroleum Institute, Nanchong, Sichuan, P. R. China. Abstract. This paper briefly discusses the following: drilling engineering system analysis principle based on the standpoints of cybernetics, information theory and system theory; drilling model theory based on fuzzy mathematics, artificial intelligence and multi-analysis theory; and optimal drilling method based on mathematical programming. The results applied to the Sheng-Li oit field and other interesting drilling problems are also discussed. Résumé. Sont brièvement décrits dans cette communication: le principe d'analyse du système d'ingénierie du forage des points de vue de la cybernétique et des théories de l'information et des systèmes; la théorie de la modélisation du forage basée sur les sous-ensembles flous, l'intelligence artificielle et la théorie de l'analyse multiple; et la méthode optimale du forage, basée sur la programmation mathématique. On indique également les résultats obtenus sur le champ pétrolier de Sheng-Li et quelques problèmes intéressants en forage.

INTRODUCTION

Drilling optimization has been studied since the 1950s in the USA. In the 1970s, Chinese engineers became interested in the subject and learned a lot from it. In order to solve the practical problems in drilling with optimization theory, first, various objective laws in drilling must be thoroughly understood, and the corresponding models must be set up correctly. Then, based on those models and some necessary constraint conditions, the solution vector that makes the objec- tive functions optimum can be worked out. Here, the first step is more important. At present, the analogue simulated experiments in the laboratory and the self-simulated tests in the field are common methods for setting up drilling models. The latter consists mainly of `Drill Off Test" and `Five-Spot Drill Test''. All are one-shot single factor simulated experiments or tests. The resultant models are examined or checked only by experience and subjective need. Since 1982, some people have gradually lost enthusiasm for drilling optimization. The main reason is that the correct ways of setting up and examining drilling models have not been found. It has been proven in practice that this problem cannot be solved satisfactorily with the above methods. The resultant models are too simple and rough to fit the objective laws in drilling, and therefore correct forecasts and decisions cannot be gained. DRILLING ENGINEERING SYSTEM ANALYSIS PRINCIPLE System engineering based on system theory, cyber- netics and information theory occupies an outstand- ing position in modern scientific methodology. It offers a type of advanced mode of thinking. From the viewpoint of system theory, the drilling course must be dealt with as a whole system, and the structure and behaviour of the system can be described through mathematical models. Her

The use of air to provide an aid Air drilling as a practical technique by which holes could be drilled has in,the oilfield came of age in the early been an interesting and sometimes complex 1950's. The obvious attraction lay in the series of events. The bulk of what has hap-potentially high drilling rates. The estab-pened pertaining to oil well drilling has lishment of air compressor rental companies be en accomplished from approximately 1950 to in the mid, 1950's in West Texas and the ' date. Characteristically, this work has Rocky Mountains was an indication..that the been a series of "ups and downs". The most use of air and gas had become an economic significant step has been in the development reality. The increasing cost per foot of of foam to extend the application of the air hole for the operators gave impetus to the techniques in locales where water influx and development of techniques which would in-hole enlargement would otherwise preclude crease penetration rates, thereby reducing the use of air.

The pdf file of this paper is in Russian.

Horizontal drilling and sidetracking of existing wellbores is one of the main methods of production level increase on brownfields. This paper describes the engineering study on drilling performance enhancement conducted for a group of oilfields in Western Siberia, Russia, where the operator company has just started sidetrack and horizontal drilling campaign.

The first several sidetracked wells drilled were characterized by high amounts of non-productive time (NPT) due to downhole tools failures and low penetration rates (ROP). For NPT root cause analysis, drilling surface logging data (including real-time torque and drag analysis) along with downhole measurement while drilling (MWD) vibrations data was analyzed and figured out the failures mechanisms. ROP improvement process included interpretation of LWD and wireline logs and their correlation with bottomhole assembly (BHA) performance via mechanical specific energy (MSE) approach.

A number of factors that led to overall unsatisfactory performance on sidetracks were identified. This included wrong bit selection, limited drilling parameters, hole quality problems and cleaning issues and several others. These issues were properly addressed with field-proven drilling optimization process, which resulted in doubling of previously achieved ROP and elimination of NPT. The next sidetrack was drilled with 40% reduction of average rig days per 1000 m. Based on experienced gained, a motorized rotary steerable system (RSS) BHA was selected for the next complex sidetrack well, and provided another record-breaking performance, with another 20% improvement of ROP. The successful techniques are currently being transferred from sidetracks to horizontal sections on new wellbores.

The paper represents latest achievements of ongoing drilling optimization process, which allowed the operator company to significantly decrease time and operational costs on drilling operations. The described complex geological and technological approach, along with revised wellbore placement, have led to main project performance indicators increase and next-step completion and production solutions for enhanced hydrocarbons recovery.