Abstract

In Japan, natural gas that has been dissolved in water is mainly produced by gas lifted through a perforated casing. Since abnormal formation pressure causes abnormal cross flow among production sections, a technique for sealing the sections with abnormal formation pressures is required, in order to increase natural gas production. In this study, we propose a new drilling technique for the fresh sealing cement using waterjet. Preliminary laboratory drilling tests were conducted under air condition to clarify the fundamental drillability of a waterjet for the purpose of sealing cement. The main results obtained in this study can be summarized as follows:

  1. The waterjet has a good drilling performance for the fresh sealing cement.

  2. The suitable aging time before sealing cement for drilling should be determined based on the mechanical properties required for sealing the sections with abnormal formation pressures.

1. Introduction

In the South Kanto natural gas fields of Japan, natural gas that has been dissolved in water is mainly produced by gas lifted through a perforated casing that serves as production tubing. In this gas field, the typical length of a production zone in a production well is several hundred meters. Since abnormal formation pressures cause abnormal cross flows [1] among production zones, it is important to select the appropriate production zone to prevent the gas flow from developing cross flow [2]. However, such cross flow often occurs during the lengthy gas-production process. Therefore, a technique to seal the sections with abnormal formation pressure is required, both to prevent cross flow and to increase the production of natural gas.

The conventional sealing technique calls for cementing the target formation that has caused the cross flow. After the cement has cured, the cured cement is drilled out with a drill bit, an operation that requires a large drilling facility. A lighter drilling system suitable for use with sealing cement is needed. In this study, we propose a new drilling technique for fresh sealing cement in using a waterjet. Preliminary laboratory drilling tests were conducted under air conditions to clarify the fundamental drillability of a waterjet for the fresh sealing cement. The drilling performance related to the cement sealing and the suitable curing time for the sealing cement needed before drilling are discussed in this paper.

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