Abstract

This paper presents the results of a project, which was initiated for analyzing the inflow performance and inflow distribution of one smart and two problematic conventional, long and tortuous horizontal wells in Brunei. 

Following a detailed hydraulic analysis of these wells, a good match with the field measurements was obtained. Simulation results show that the problems in the conventional wells were not as severe as those interpreted from the measurements of distributed temperature sensing systems (DTS). It is also demonstrated that the compartmentalized completion with inflow control valves (ICV) in the smart well has added value, as the well would not be producing from the half of the reservoir section without the smart completion.

Introduction

Brunei Shell Petroleum Cooperation (BSP) is a keen implementer of wells with sophisticated trajectories for achieving maximum reservoir exposure. The aim is to drain oil from stacked sand bodies, which cannot be economically produced via separate dedicated wells. These sophisticated wells have long reservoir sections up to 3 km with undulations up to 40 m. Some of them are equipped with distributed temperature sensing technology for monitoring the inflow distribution, and some have smart completions to control inflow from different reservoir sections and assist well clean up. Interpretation of the DTS traces indicated inflow performance problems in the long conventional producers, whereas the smart wells were observed to be flowing from more or less their full length. Inefficient well clean up was thought to be the primary cause of the inadequate inflow performance in the conventional wells. Therefore, a detailed hydraulic analysis of two problematic conventional wells and one smart well was requested by BSP to understand the inflow problems in the conventional producers and to confirm the justification of smart completions.

Since the well initial kick-off and clean up are highly transient processes¹, an appropriate transient multi-phase flow simulator was used for modelling. The wells were simulated from initial start-up until early in their production life, which includes mud removal and stabilized wellbore flow. In both conventional wells, calculated flow rates and pressures agreed with the available well test measurements. Simulation results have shown longer producing intervals than those derived from the DTS traces. The main reason for this could be that the limited flow coming from the toe section in a horizontal well causes a minor temperature disturbance, which can easily be overseen in the DTS traces². Good results, which were obtained from the initial calculations, gave enough confidence to continue with the smart well, which is a more complicated case from the modelling point of view.

Since the smart well had not been tested in the early stages of production, only the recorded pressures from the permanent down hole pressure gauge were used for validating the model. Calculated flowing bottomhole pressures agreed with the measurements. Simulations have shown that the smart completion gives an opportunity to produce the well from the full length. A sensitivity analysis was performed by removing the smart completion from the model. Results justified the smart completion, as the well would not be producing from half of the reservoir section if it were completed conventionally.

Results of this work have provided enough confidence to use the same modelling approach in design and operation of future wells with complicated trajectories and architecture. This modelling approach could also be of value for more adequate interpretation of DTS measurements, and understanding how the smart completion helps increasing the producing interval over a long well section.

Well Information

All three wells have long reservoir sections ranging from 1.1 km to 3 km with undulating elevation profiles for intersecting different reservoirs. The two conventional wells, W1 and W2 have fairly simple completions. They are both equipped with DTS systems, and only one of them has a permanent down hole pressure gauge. Details of their completions and elevation profiles are given in the following sections.