Sometimes decline curves for tight gas wells indicate that linear flow may last for over 10 or 20 years. These decline curves may show outer boundary effects but no pseudo-radial flow. This paper presents decline curve analysis methods for such wells. Values for k xf and drainage area can be calculated. Stabilized (bounded) flow equations are also presented for forecasting. The solutions and type curves developed are for both infinite-acting and stabilized flow with either constant Pwf or constant rate. Several field cases are shown with example calculations. P. 265

This paper was selected for presentation by an SPE Program Commdtee following rwew of information contahed in anqbstract submitted by the author(s). Contents cd the paper, as -fed. * n~~0 M* by Me .%cw@ d Petroleum Engineam and are subject to corr~on by the atithor(s) lle material, as presantad, does not necessarily reflect any position of the Sochty C4Ps4roleum Enginaars, its officers, or members Papers presented ad SPE meetings are subject to publication review by Editorial Commtiees of the Society of Petroleum Engineers Electronic reproduction, distitbution, or storage of any pati of ttws paper for mrnmercial purpasea wthout the wrilten consent of the Scmety of Petroleum Engineers is pmhibifd Permission to reproduce m print is restricted to an abstract of not more than S02 words, illustrations may not ba mpmd l%e abstract must contain conspicuous acknwhdgment C# where and by whom the paper was presented Write Librarian, SPE. PO, 130xS3S93%, Richardson. TX 7S0S3-3.536, U S A , fax 01 -972.9S2-943S AbstractLinear flow may be a very important flow regime in fractured gas wells. It is also important in some unfractured wells. This paper presents practical approach to analyze both pressure (well testing) and production rate (decline curve analysis) data which is influenced by linear flow, The paper explains two approaches to analyze the data (hand calculations and curve fitting). It uses analytical solutions that are adapted to different reservoir models. These models include fractured wells and wells producing reservoirs with high permeability streaks. Permeability, flow area, and pore volume may be obtained from either pressure or production rate data. The constant rate solutions are different from the constant pressure solutions, The use of the wrong equations in the analysis may result in errors as high as 600A,The paper also shows the application of these techniques in analyzing field data.

The productivity of the wells in a moderately rich gas condensate reservoir was observed to initially decrease rapidly and then increase as the reservoir was depleted. All wells in the field showed the same response. Compositional simulation explained the reasons for these productivity changes. During early production, a ring of condensate rapidly formed around each wellbore when the near-wellbore pressures decreased below the dew point pressure of the reservoir gas. The saturation of condensate in this ring was considerably higher than the maximum condensate predicted by the PVT laboratory work due to relative permeability effects. This high condensate saturation in the ring severely reduced the effective permeability to gas, thereby reducing gas productivity. After pressure throughout the reservoir decreased below the dew point condensate formed throughout the reservoir, thus the gas flowing into the ring became leaner causing the condensate saturation in the ring to decrease. This increased the effective permeability of the gas. This caused the gas productivity to increase as was observed in the field. There were also changes in gas and condensate compositions in the reservoir which affected viscosities and densities of the fluids. These effects also impacted gas productivity. This work is another step forward in our understanding of the dynamics of condensate buildup around wellbores in gas condensate fields.

No abstract