South Sulige block, located in the Ordos Basin in China, is classified as Tight Gas Reservoirs with permeability ranging from 0.01 md to 2 md and porosity rarely exceeding 10%. Potential gas production intervals were identified in the Shihezi Formation and Shanxi Formation.
Four of the existing hydraulically fractured wells, were re-tested by Total.
Total drilled four new wells on this block, stimulated them with hydraulic fractures and performed extensive tests.
The main objectives of well testing were:
To reduce the uncertainties on well productivity, mainly permeability and skin.
To characterize reservoir extension: no flow boundaries, channel width.
To estimate the dynamic connected volumes which are linked to the extent and interconnectivity (amalgamation) of the sand bodies (fluvial sand bars/channel width).
Extended dual build-up tests were designed (from 8 to 18 months) ended by a long duration build-up (from 3 to 10 months) to characterize well productivity and connectivity. As no signature of radial flow, appeared on derivatives, permeability-thickness values were strongly uncertain. Dual build-up tests were designed to allow us to reduce uncertainties on permeability-thickness product. The test analyses have revealed the presence of channel margins to match transient depletion between build-ups.
The results of these extended tests highlighted that channel widths determined by pressure transient analysis were much smaller than expected, compared to outcrop description, except for one well (Y3). This implies that internal heterogeneities, not visible on outcrops, play a major role in the well drainage. These results have to be taken into account to optimize the development scheme, combining the good productivity in the Y3 area and more standard well behaviour elsewhere.
