Slimhole Drilling Cuts Development Costs of Low Permeability Oil Field With Great Margin
Authors: Zhang Fengmin , Dong Jie , Cui Yueming , Wang Li 
Published: December 2007

Abstract
Most of unmobilized oil in situ in Jilin Oilfield are in low permeability reserves. How to improve the efficiency of development has become a key subject in the process of development of the field. In recent years, to reduce development costs, some beneficial attempts have been made to tap the low permeability reserves through slim hole drilling. Practices show that slim hole drilling can offer significant savings in well drilling costs. This paper summarizes and evaluates slim hole drilling technology and its economic feasibility. Focusing on the oil & gas reservoir with different burial depth, the paper also presents details of four aspects affecting drilling costs, which include drill rig operating expenses and application of the new concerned technology. The ways of applying slimhole drilling matched technology is identified as one of effective means of cutting development cost of low permeability oil fields.

Introduction
The proven unmobilized oil in situ in Jilin oil field amount to 320million tons, among which the low permeability reserves account for 92.4%. The low permeability reserves are important reserved resources to maintain the oilfield continuous sustainable development, how to effectively explore and develop these parts of oil reserves is a key study subject for us. The critical point to probe the low permeability reserves lies in if we could solve these problems including the low productivity per well, high production cost and large infrastructure investment scales properly. In order to cut down drill cost and explore an effective method to develop the low permeability oil field, in 1992-1997, Jilin Oilfield carried out a series of concerned slimhole drilling matched trial studies. Field trials indicate that saving of drill cost and reduction of investment scale have been realized, thereby it can be seen that slimhole drilling technique is one of the principal means to improve the low permeability economic proficiency.

Characteristics of low permeability reservoir and the distribution of development wells
Petrophysical Characteristics and its impact on oil well production.
The low permeability reservoirs in Jilin oil Field can be mainly characterized as narrow pore throat, poor permeability, and low natural producing energy. Some particular blocks even have no natural producing energy. Taking the typical low permeability reservoirs in Xinmiao Block of Jilin Oil Field as an example, the pore throat radius is usually 0.1-4µm, rock particle size is small and fine. The layers have a 9-16% porosity and 12% average porosity, and sandstone layers with a 0.1-8×103µm2 permeability and 1.2×10-3µm2 average permeability. The natural producing energy is nearly zero, thus fracturing and reforming the reservoir have become a necessary procedure of bringing the oil well into production.

Distribution of Development Well
The low permeability reservoirs with the well depth varing from 500m to 2400m are widely distributed in Jilin Oil Field.

Petrophysical Characteristics and its impact on oil well production
The low permeability reservoirs in Jilin oil Field can be mainly characterized as narrow pore throat, poor permeability, and low natural producing energy. Some particular blocks even have no natural producing energy. Taking the typical low permeability reservoirs in Xinmiao Block of Jilin Oil Field as an example, the pore throat radius is usually 0.1-4µm, rock particle size is small and fine. The layers have a 9-16% porosity and 12% average porosity, and sandstone layers with a 0.1-8×103µm2 permeability and 1.2×10-3µm2 average permeability. The natural producing energy is nearly zero, thus fracturing and reforming the reservoir have become a necessary procedure of bringing the oil well into production.

Distribution of Development Well
The low permeability reservoirs with the well depth varing from 500m to 2400m are widely distributed in Jilin Oil Field.