Estimation of Critical Drawdown Pressure of Sand in Gas Wells Applying Geomechanical Analysis: Case Study Dragon Field, North of Paria

Rodriguez, R. A. (PDVSA) | Rodriguez, D. (PDVSA)



This study is based mainly on the Cubagua formation belonging to the Dragon field, where the intervals of interest of the deposits are poorly consolidated and the cementation of the grains of sand is poor, as to be able to withstand the efforts applied as a result of the passage of the produced fluids through them, being able to start the phenomenon of sandblasting. The realization of this work consisted of the use of the BP-Willson methodology3,6,7,9, which estimates the critical flowing bottom pressure of sanding (BHPc) necessary to cause instability of the rock. In function of the fact that the rock is unconsolidated (Upper Miocene-Pliocene), corrections of P and S wave readings were made by Cp, gas and hole compaction, and mathematical algorithms of probabilistic type were generated through techniques Statistics of uncertainty management using Crystal Ball of the variables Δtc as a function of RHOB for each sand. The magnitude of geomechanical properties varied depending on the type of depositional environment, tectonic stresses and depth. The static young's modulus exhibits low values lower than 1 MMlpc, typical for unconsolidated deposits (Lacy, 1996). The Poisson's ratio in the order of 0.4 indicates that these formations have a high level of deformability and compressibility. The unconfined compressive strength (UCS) correlation of McNally 1987 (Gulf Coast)12,5,2, represented with greater certainty the data from the well tests obtaining values of UCS in the order of magnitude of [789-1918] psi. The results of the maximum and minimum stresses obtained by the equations of Mathews & Kelly (1967)6,13,17,15 confirm the transverse fault stress regime (σH> σv> σh) present in the area. Finally, the critical drawdown pressures of sanding for the Dragon Field wells, with a probability of P (50) ranged between [802-1091] psi and the critical gas rates per well resulted in the order [30-245] MMscfd.