The pilot reported that while approaching an open field for landing, the balloon suddenly slowed down. Shortly after, he noticed that the balloon had contacted power line wires, and the lines were traveling down the side of the balloons envelope and uprights and trapped his passenger against the basket. The pilot stated that the passenger was able to free herself as he was able to kick the wires from the corner of the basket. The balloon subsequently ascended about 200 feet. The pilot proceeded to initiate a landing in the nearest open field and landed without further incident. The pilot further reported that neither he nor his passenger saw the power lines prior to the balloon impacting them. Examination of the hot air balloon revealed that the envelope and basket sustained minor damage; however, the passenger sustained serious injuries.