Analyzing Gas Well Productivity Change with Production in Unconsolidated Sandstone Using Rate Transient Analysis

Abstract

The primary objective of this paper is to demonstrate the changing productivity of the cased hole gravel packed gas wells due to wellbore matrix disturbance, rapid bean up operations and how daily production data (rates and flowing pressures/ temperature) can be used to analyse gas well performance along with estimation of Gas In Place. This work includes the identification of well problems and productivity changes, attributed to wellbore matrix disturbance or sub-surface issues in unconsolidated sands. The analysis method used in this work is Rate Transient Analysis along with Pressure Transient Analysis. Bottom hole temperature behavior and Decline Curve analysis are also analyzed to validate the results captured from RTA. RTA is ideal for establishing a well's productive capability early in its life (after 3-6 months) and categorizing subsequent well decline behavior as either reservoir depletion or productivity loss through time (or a combination of the two). Through interpretation of diagnostic plots, such as the Flowing Material Balance Analysis and Type Curve Analysis plots, specific productivity issues can be easily identified and classified using simple pattern recognition. Field examples from multiple gas wells across KG Offshore Deep Water (Water depth > 400m), completed with cased hole gravel pack, are included in our study. The present case study indicate the apt use of RTA, PTA and other bottom hole parameters to determine current K, changing skin & the most important GIIP of single well gas fields. RTA will supplement and to some extent give the actual estimation with less error. Deliverability issues such as wellbore matrix disturbance and gravel pack degradation associated with unconsolidated sands are identified. The issues has been validated by flowing temperature behavior. Results show how RTA can be used as a practical screening tool, identifying underperforming wells and quantifying the potential benefits of remedial action based on remaining reserves. This paper presents a novel application for RTA - as a screening tool for diagnosing underperforming wells and estimating their optimum producing rates. The industry tends to undervalue the potential benefit of all but the simplest remedial measures for underperforming producing wells for two reasons- 1. Poor performance is often simply accepted as a statistical reality and 2- operators do not even realize that their wells are underperforming. In case of deep water, work over job or drilling new well is a very costly affair. Also, time plays a major role in economics of a development project. If the issue(s) can be resolved, production improvements aggregated field-wide could have tremendous economic implications.