Improved DTS profiling model for horizontal gas wells completed with the open-hole multi-stage fracturing system

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Highlights

  • Open-hole packer completion style causes a featured DTS data profile.

  • Double temperature drops observed at the fracture and frac port locations.

  • A simulation sub-region representing the open-hole annular space is essential.

  • Gas production rate and frac port location dominate temperature data behavior.

Abstract

The fiber-optic distributed temperatrue sensor (DTS) has been used for flow profiling in horizontal multi-stage fractured wells, and several reservoir/wellbore coupled thermal models were developed. Although these theoretical models are applicable only to some specific scenarios, the industry has realized the great potential of DTS for production prediction in unconventional resources. This paper presents a DTS flow profiling case for a horizontal multi-stage fractured well in tight gas reservoirs with open-hole packer completion scenarios by applying a newly improved theoretical model.

In this paper, we extended the conventional semi-analytical wellbore-fracture-reservoir coupled flow/thermal model which have been developed for cased, perforated, and multi-stage fractured wells, by considering the special feature of the openhole packer completion scenario. Since the formation fluid flows first through the fracture into the open-hole annular space between the formation and the production liner, and then flow along the annular space until meeting the frac port on the production pipe, a simulation sub-region was added for representing the open-hole annular space, which helps to understand the flow and heat transfer inside it. The presented model successfully simulated the two-segment flow regime caused by the simultaneous flow and heat transfer in the annular space and the production pipe. In each stage, the DTS temperature data possibly show double drops due to the Joule-Thompson cooling effects at the fractures and frac ports if their locations are not consistent.

With the improved model, the synthetic cases were firstly used for studying the temperature characteristics and the effects of gas production rate and frac port location. Then the DTS monitoring data during a three-rate production test in a horizontal multi-stage fractured well in the Erdos Basin of China was simulated and analyzed. The open-hole packer completion was taken into account in the simulation and the gas rate prediction is satisfactory.

Section snippets

Credited author statement

Weibo Sui: Model establishment and paper writing. Di Zhang: Model programming. Si Cheng: Formal analysis. Qilin Zou: Field data collection. Xiaosong Fu: Formal analysis. Zehao Ma: Validation

Mathematical model description

Fig. 1 shows the completion diagram of a horizontal multi-stage fractured well with openhole packer completion. The formation fluids firsly enter the annular space from hydraulic fractures, then the fluids flow into production pipe when arriving at the frac ports. The fluid temperature in the production pipe is monitored by a coiled tubing conveyed DTS equipment. To simulate the temperature monitored by DTS and inverse gas flow profile, the following mathematical models were established. The

Synthetic cases

With the presented mathematical model, the temperature behavior of a horizontal multi-stage fractured well with openhole packer completion was studied, and the effects of gas rate and frac port location were investigated by using synthetic cases. Through the following cases, the reservoir and fluid properties are all kept the same. The horizontal well is isolated to be four stages for illustration, and there is single transverse fracture whithin each stage. The fracture lengths of different

Field application

By adding a sub-region of annular space, the improved model could be used to simulate the flow and heat transfer more accurately for a horizontal multi-stage fractured well with openhole packer completion. Here we apply the presented model to interpret the temperature data monitored by DTS during a post-fracturing production test for gas rate profiling.

The horizontal well was producing gas from a tight sandstone reservoir in the Erdos Basin, China. With the openhole packer completion, the well

Conclusion

We have presented a temperature prediction model for a horizontal multi-stage fractured well with openhole packer completion. Compared with the existing models, the presented model added a simulation sub-region representing open-hole annular space, which could help to simulate the flow and heat transfer caused by the inflow from fracture and outflow into production pipe. The presented model was used for investigating the temperature behavior of the two-segment flow regime in synthetic cases,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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