Abstract

A field study was performed to investigate the flow behavior in a horizontal well and its interaction to the reservoir.

A horizontal well was drilled in a heterogeneous reservoir with fractures at undersaturated reservoir condition at the Yurihara oil and gas field in Japan. In order to investigate the fluid influx distribution, the pressure and fluid density distributions along the horizontal well, PLT logging, was run into the wellbore.

A comprehensive model and computer program, POPHOZN was also used as a tool to discuss key parameters affecting the steady-state production behavior of the horizontal well.

The followings have been concluded as parts of the present study on the analysis of flow behavior due to confluent fluid influx along the horizontal well:

  1. Field data such as fluid influx distribution as well as pressure and fluid density distributions were successfully acquired along the horizontal well. The analysis of the production logging data clarified the production behavior of the Yurihara SK-15.

  2. It was found that the gas-oil two-phase flow was encountered in the horizontal wellbore due to saturated conditions. The characteristics of the two-phase flow could be reasonably accounted for calculating pressure drop and fluid density distribution in the horizontal well by the POPHOZN.

  3. The analysis of the production logging data demonstrated that overall performance of the POPHOZN successfully simulated the interaction between the heterogeneous reservoir and the horizontal well configuration, and the flow behavior along the horizontal well could be physically expressed.

Introduction

Horizontal wells have become attractive for the production of thin-layer reservoirs, naturally fractured reservoirs, and reservoirs with gas- and water-coning problems. Horizontal wells can improve the productivities of oil and gas reservoirs compared to conventional vertical wells due to the enhancement of the reservoir contact and negative skin factor.

The assumption of a constant pressure along a horizontal wellbore is used often for well test analysis and reservoir engineering. It can be reasonable when the horizontal wellbore pressure drop is very small as compared to the pressure drawdown. In contrast, if the pressure drop along the horizontal wellbore is significant as compared to the pressure drawdown, the pressure drop along the horizontal wellbore can not be ignored. This is especially true for highly productive reservoirs with limited pressure drawdown, the reservoirs with small inside diameter wellbores, or when gas-liquid two-phase flow is encountered in the horizontal wellbore. In these situations, the pressure drop in the horizontal wellbore and its interaction with the reservoir are the crucial items of information for proper design of the horizontal well with regard to production performance, as well as well completion.

The flow in a horizontal wellbore has two different characteristics from those in pipelines and vertical wells, which are the flow behavior with an increasing flow rate along it due to influx from the reservoir, and the relationship between the pressure drop and the influx (Fig. 1).

Literature Review. Many dedicated researches on this subject have been conducted experimentally and theoretically.

Dikken presents a simple analytical method that links a single-phase turbulent liquid flow in a horizontal wellbore to an isothermal reservoir flow and predicts the frictional pressure drop along the horizontal wellbore. He concludes that the reduced drawdown caused by turbulent flow along the wellbore may result in the total production rate reaching a certain critical values as a function of wellbore length.

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