High resolution temperature data were used to identify the formation of condensate in the rock matrix and the subsequent developing banks of condensate in a highly layered gas condensate reservoir, during an appraisal drill stem test (DST). Condensate blockage leads to reduced gas productivity and loss of production of the more valuable, heavier components. Understanding this phenomenon is not only important for the transient analysis of the DST pressure data, but also for the future production plan of the field.
A multiple discrete temperature sensor array (MDTS), run on TCP guns across a perforated interval, enabled consecutive real-time recordings of wellbore temperature profiles to be made throughout the whole duration of a DST, at high temporal, spatial and thermal resolutions. These transient data were used to create a detailed 3D map of the wellbore thermal response. Using this technology, simultaneous Joule-Thomson heating of liquid condensate and cooling of lean gas entering the wellbore from various layers were identified.
By continuous monitoring of the temperature profiles across the perforated interval, liquid condensate dropout in the near-wellbore rock formation was identified. The reservoir consists of thin sand beds, separated by shaly layers, which provided an upper and lower boundary to contain the separated gas and liquid condensate. In each layer, there are two phases; lean gas exhibiting Joule-Thomson cooling, and liquid condensate exhibiting Joule-Thomson heating. A continuous reduction in productivity index throughout the flow period provided supporting evidence of the formation of a condensate bank, causing a reduction in gas relative permeability. During the shut-in periods, the high-resolution temperature sensors detected a growing column of warm liquid condensate in the wellbore. At the near-wellbore region, the condensate bank collapsed under the influence of gravity and wept into the wellbore. Pressure gauges below, above and in the middle of the perforated interval confirmed the density of the condensate column, rising in the wellbore.
Unlike other cases using synthetic data, this case study is based on real field data. Discrete temperature sensors across the producing interval, gave valuable information therefore making a significant contribution to the future field development plan.