In deviated wellbores, the relationship between friction pressure and hydrostatic pressure differs from that in vertical wellbores. The change in this relationship increases the need for accurate slurry friction pressure modeling. Because of deviation, incremental slurry friction pressure changes are more significant than incremental changes in hydrostatic pressures. Real-time calculation of an accurate bottomhole treating pressure in deviated wellbores is more difficult to achieve, than in vertical wells, because of the lack of accurate slurry friction models.
"Abnormal" surface treating pressures, which are caused by this change in relationship, were recorded while fracturing deviated wells in the Prudhoe Bay Field in Alaska. The significance of this relationship is presented along with observed slurry friction pressure data obtained through the use of bottomhole pressure recorders. A methodology and mathematical model for more accurate calculation of slurry friction pressure is presented for these conditions.