ARTICLES

References

Compared with the traditional operating system, oil–gas multiphase transportation technology has several obvious advantages.¹ As the key part of the production system, a multiphase pump can decrease wellhead back pressure, enhance oil output, reduce investment cost, simplify the technological process of production and increase well service life.² The crude oil in the Kuidong region of the Liaohe Tanhai oilfield is characterised by a high gas:oil ratio (GOR), high oil viscosity, high density, high content of colloidal asphalt, low content of wax and low freezing point. In the shallow region, the strong current, high content of silt and drift ice in winter have brought great challenges to offshore construction. The total length of the pipeline is 20 km: 15 km was buried subsea, 3.5 km was buried along the sea wall road and 1.5 km was buried onshore. On the basis of a practical production status, the scheme of developing oil–gas multiphase transport was studied. It can provide technical support to construction and exploitation and ensure safe transportation in the Liaohe Tanhai oilfield.

Physical Property Analysis of Crude Oil
Recently, the prominent characteristics of the Kuidong region have been that the GOR is high and the associated gas is mainly methane: the average content of methane is 88.02 %, ethane 5.51 % and propane 2.24 %. Table 1 shows the crude oil properties. It can be seen that the oil is heavy oil and the wax content and freezing point are low. Especially, the freezing point of crude oil produced from some particular wells is -24.8 °C.

The rheological characteristics of crude oil with a different GOR at different temperatures have been tested in the laboratory. From the test results, it is obvious that with an increase in GOR, the viscosity is reduced, but the range of viscosity is 1.6–93.85 mPa.s. This is because the rheological characteristics of oil with a low wax content are mainly influenced by the GOR at certain temperatures. Figures 1 and 2 are the rheological characteristic curves.

Feasibility of Multiphase Transportation Technological Process
The transportation system of the Kuidong region is shown in Figure 3. The length of multiphase pipeline between platforms 2 and 1 is 2 km and the nominal diameter is 168.3 mm. The length of multiphase pipeline from platform 1 to the terminal systems onshore is 20 km: 15 km was buried subsea, 3.5 km was buried along the sea wall road and 1.5 km was buried onshore, and the nominal diameter is 219.1 mm.

To read full article please click here.