Production improvement of hydraulically fractured wells in tight gas plays in Pakistan

Research output: ThesisMaster's ThesisResearch

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Abstract

Tight gas reservoirs contain a significant potential for dry gas production including one big problem: Tight gas reservoirs, having a very low permeability do normally not produce at economic limits. In general tight gas fields are defined as having less than 0.1 millidarcy (mD) matrix permeability and very low porosity (less than ten percent). This special setting is the reason why this fields are normally not economically producible. The common approach to get rid of this is hydraulic fracturing to stimulate the drilled wells. OMV is currently active in gas fields in Pakistan (Miano and Sawan) and holding interest in tight gas production. Several wells which had been drilled are producing dry gas below economic limit. As a typical treatment the wells drilled in the Sawan and Miano tight gas fields were stimulated via hydraulic fracturing. Contrary to the expectations the wells started to produce water comprising gas instead of pure dry gas although the fact that the geology indicates no aquifer in this area. Typically tight gas wells are producing dry gas at low rates. This was also the case before the wells were hydraulically fractured in Sawan and Miano field. After the fracturing job, the gas rate increased first but so did the water rate until a point where the amount was so high that the eruptive lifting energy was exceeded and the gas rate went down to zero. The aim of this thesis is the investigation of the source of water inflow and furthermore the declaration of the amount of the unwanted fluid flowing to each well. First step was to get an insight into the complex structure of the field and get an overview of all the work done in the past. Afterwards the core measurements were conducted and plotted for a better understanding of the reservoir. There I discovered an unusual porosity behaviour for this kind of water wet sandstone reservoir. It shows a bimodal pore size distribution which means that there are two dominant pore sizes present in the reservoir rock- micro pores in the range of 0.02 to 0.1 µm and macro pores with average pore size of one magnitude higher than the small ones. This was the trigger to start investigating a so called micro pores feeding effect. At a certain pressure drop the water blocked in the small pores gets released and feed into the bigger (gas filled) pores. So instead of gas, water is produced as long as water is available in the small pores. As the measurement showed an average water saturation of around 40% this is quite a lot. In parallel also the possibility of the fracture growth into a water bearing neighbouring layer was observed. To clarify the water source a simple generic model was build and fed with measured field data. 

Details

Original languageEnglish
Supervisors/Advisors
Award date16 Dec 2016
StatePublished - 2016