fluids bulk modulus
            Klb  = this.liquidFluid.K;
            Kgb  = this.gasFluid.K;
            % Gas saturation degree
            Sg   = 1.0 - Sl;
            % Capillary pressure
            pc = pg - pl;
            % Derivative of the liquid saturation degree wrt pc
            dSldpc = this.capillaryPressure.derivativeSaturationDegree(pc, this.porousMedia);
            % Compressibility coefficients
            cll = Sl * ((biot - phi) / Ks) * (Sl + dSldpc * pc) - phi * dSldpc + phi * Sl / 