The Methods Taken in SZ36-1 Oilfield in the Early Stage of Production
Authors: Hongwen Yu , Bo Li 
Published: December 2007

SZ 36-1 Oil Field is located in Liaodong Bay of Bohai Sea and is an unconsolidated sand and structure-lithology reservoir. The reservoir is distributed in Paleogene Lower Dongying Formation at the depth of 1300-1600m and dominated by "channel mouth bar" of delta-front deposit with stable distribution and good connectivity. The crude oil is heavy and viscous. The field has total oil-bearing area of 43.3km2 and recoverable oil reserve of 65×106m3. The pilot areas AII, AI, B and J were put into production successively after September 1993. Some effective practices were performed in early development stage of the pilot areas. Good examples of these are pre-gravel pack ensured long term normal production of oil wells; the use of electrical submersible pump (ESP) increased the oil producing thickness and realized high speed development; fully utilizing natural energy and timely starting water injection extended low water cut period; the early reservoir damage study and effective measures increased the production; the geological studies during development improved the understanding of the oil field; the reservoir numerical simulation technology is used to track the production performance of the oil field and so on. All these practices have led to good development results.

Introduction

Oil Field Geology

SZ36–1 oil field is located in the middle of Liaoxi Low Uplift in Liaodong Bay of Bohai Sea, China. It is an NE striking Paleogene drape structure developed on basement of burial hill, which is bounded by Liaoxi main fault in the northwest and has the slope in the southeast plunging into Liaozhong sag (Fig. 1).

The field is 102km from Qinhuangdao city and 46km from coast of Suizhong County. The field is at water depth of 32m and has icing period of 30 days with perennial temperature variation in range of –18~38°C. The reservoir is distributed in lower Dongying Formation with buried depth of 1300-1600m and can be divided into 4 oil groups O, I, II and III. The oil groups I and II are main pay zones and are subdivided into 8 layers and 6 layers respectively (Fig. 2).

The reservoir is mainly fine sandstone and belongs the deposits of channel mouth bar, subaqueous channel and lake shoal microfacies of delta front facies. The reservoir, with stable distribution and good connectivity, consists of multi-layers sandstone and several sets of sand-mud interbeddings. The individual sand layer is 0.5-15m in thickness and characterized by upward -coarsening. The sand is unconsolidated and loosely mud-cemented with porosity of 29-35% (average of 32%) and permeability of 100-10000×10-3µm2 (average of 2600×10-3µm2). Each oil group has its own oil-water system. SZ36–1 oil field is a layered sandstone reservoir controlled by structure and lithology. The field has total oil bearing area of 43.3 km2 and recoverable oil reserve of 65×106 m3 (oil original in place is close to 0.3×109m3).

Fluid Properties.

The crude oil of SZ36–1 oil field is characterized by high viscosity, high density, high gum and asphalt contents, low sulphur content, low wax content and low solidification point.

Surface oil density: 0.941 - 0.997g/cm3, average 0.962 g/cm3;

Formation oil viscosity: 13 - 380mPa.s, average 70mPa.s;

Original reservoir pressure: 14.3MPa;

Saturation pressure: 8.5 - 13.3MPa, average 12.0MPa;

Original dissolved gas-oil ratio: 23-38 m3/m3, average 30 m3/m3;

Volume factor: 1.0700-1.1132, average 1.0964;

Reservoir temperature: 62 - 64°C;

Average wax content: 2.9%;

Average sulphur content: 0.35%;

Average asphalt content: 8%;

Average gum content: 35.7%;

solidification point: -13.4°C;

Oil Field Geology

SZ36–1 oil field is located in the middle of Liaoxi Low Uplift in Liaodong Bay of Bohai Sea, China. It is an NE striking Paleogene drape structure developed on basement of burial hill, which is bounded by Liaoxi main fault in the northwest and has the slope in the southeast plunging into Liaozhong sag (Fig. 1).

The field is 102km from Qinhuangdao city and 46km from coast of Suizhong County. The field is at water depth of 32m and has icing period of 30 days with perennial temperature variation in range of -18~38°C. The reservoir is distributed in lower Dongying Formation with buried depth of 1300-1600m and can be divided into 4 oil groups O, I, II and III. The oil groups I and II are main pay zones and are subdivided into 8 layers and 6 layers respectively (Fig. 2).

The reservoir is mainly fine sandstone and belongs the deposits of channel mouth bar, subaqueous channel and lake shoal microfacies of delta front facies. The reservoir, with stable distribution and good connectivity, consists of multi-layers sandstone and several sets of sand-mud interbeddings. The individual sand layer is 0.5-15m in thickness and characterized by upward -coarsening. The sand is unconsolidated and loosely mud-cemented with porosity of 29-35% (average of 32%) and permeability of 100-10000×10-3µm2 (average of 2600×10-3µm2). Each oil group has its own oil-water system. SZ36–1 oil field is a layered sandstone reservoir controlled by structure and lithology. The field has total oil bearing area of 43.3 km2 and recoverable oil reserve of 65×106 m3 (oil original in place is close to 0.3×109m3).

Fluid Properties

The crude oil of SZ36–1 oil field is characterized by high viscosity, high density, high gum and asphalt contents, low sulphur content, low wax content and low solidification point.

Surface oil density: 0.941 - 0.997g/cm3, average 0.962 g/cm3;

Formation oil viscosity: 13 - 380mPa.s, average 70mPa.s;

Original reservoir pressure: 14.3MPa;

Saturation pressure: 8.5 - 13.3MPa, average 12.0MPa;

Original dissolved gas-oil ratio: 23-38 m3/m3, average 30 m3/m3;

Volume factor: 1.0700-1.1132, average 1.0964;

Reservoir temperature: 62 - 64°C;

Average wax content: 2.9%;

Average sulphur content: 0.35%;

Average asphalt content: 8%;

Average gum content: 35.7%;

solidification point: -13.4°C;