Petrodleum origin and accumulation in basin evolution is governed by a system of nonlinear partial differential equations. The mathematical model considered comprises (1) fluid flow (2) heat transport (3) porosity of the media. The pressure, Darcy velocity and temperature are approximated by the finite element method. Optimalorder convergence in L2 and H1 is proved.

Infusing water into oil reservoir by high-pressure pump to squeeze the oil residual out of oil wells is a problem of two-phase immiscible flow displacement. The mathematical model of the problem is the initial bocmdary problem of systems of partial differential eqastions. We set up some computation schemes of the discrete operator method, and study approximation and convergence theory. Computation of the model problem yielded satisfactory results.