As a loose sandstone reservoir, PL oilfield has been characterized by its strong velocity sensitivity,long oil?bearing intervals,multiple oil?bearing sequences and complicated sedimentary types.Due to the previous failures of earlier application,horizontal well has always been considered to be not suitable for PL oilfield.Based on the micro reservoir characteristics of PL oilfield in Bohai Sea,the evaluation technology of horizontal well in loose sandstone and the classified development technology of combined well pattern in thick thin multi?layer reservoir are studied by means of seepage theory,numerical simulation and field practice.The results indicates that,the unit area velocity of the cylinder hemispherical combination seepage area of the horizontal well is far less than that of the cylinder seepage area of the directional well in the near well zone.The field test data proves that horizontal wells have more advantages in resisting velocity sensitivity in unconsolidated sandstone reservoirs.The interference between directional well and horizontal well in the combined well pattern of multi?layer thick thin reservoir is compared.It is proved that whether the formation energy is sufficient or not is the main controlling factor of inter well interference in the combined well pattern during the period of middle and high water content.