اراﺋﻪ ﻣﻌﯿﺎري ﺑﺮاي ﺗﺨﻤﯿﻦ ﺣﺪاﻗﻞ و ﺣﺪاﮐﺜﺮ ﻓﺸﺎر ﻓﺮوﺗﻌﺎدﻟﯽ ﮔﻞ ﺣﻔﺎري در ﻣﺨﺎزن ﮐﺮﺑﻨﺎﺗﻪ اﯾﺮان

A criterion to estimate the minimum and maximum underbalanced pressures of drilling mud in Iranian carbonate reservoirs

اﻫﻤﯿﺖ ذﺧﺎﯾﺮ ﻃﺒﯿﻌﯽ ﻧﻔﺖ و ﮔﺎز در دﻧﯿﺎي اﻣﺮوز و ﻏﯿﺮ ﻗﺎﺑﻞ ﺗﺠﺪﯾﺪ ﺑﻮدن اﯾﻦ ذﺧﺎﯾﺮ، ﺑﮑﺎرﮔﯿﺮي روش ﻫﺎي ﺑﻬﯿﻨﻪ در ﺣﻔﺎري و ﺑﺎزﯾﺎﺑﯽ از اﯾﻦ ﻣﺨﺎزن را اﻣﺮي ﺿﺮوري و اﺟﺘﻨﺎب ﻧﺎﭘﺬﯾﺮ ﺳﺎﺧﺘﻪ اﺳﺖ. ﺣﻔﺎري ﺑﺎ ﻓﺸﺎر زﯾﺮ ﺗﻌﺎدل در واﻗﻊ ﺑﻬﺘﺮﯾﻦ روش ﺑﺮاي ﺣﻔﺎري ﻣﺨﺎزن ﻧﻔﺘﯽ ﻣﯽﺑﺎﺷﺪ ﮐﻪ ﻓﺸﺎر آن ﻫﺎ ﺑﻪ دﻟﯿﻞ ﺗﻮﻟﯿﺪ روزﻣﺮه ﮐﺎﻫﺶ ﯾﺎﻓﺘﻪ اﺳﺖ؛ زﯾﺮا ﺣﻔﺎري ﺑﻪ روش ﻓﺮاﺗﻌﺎدﻟﯽ ﺑﺮاي دﺳﺘﯿﺎﺑﯽ ﺑﻪ ﻣﺨﺰن ﺑﺎﻋﺚ ﺑﺮوز ﺿﺎﯾﻌﺎت ﺑﺴﯿﺎر زﯾﺎد و ﻫﻤﭽﻨﯿﻦ اﻓﺰاﯾﺶ ﻫﺰﯾﻨﻪ ﻫﺎ ﻣﯽ ﺷﻮد. ﺣﻔﺎري ﻓﺮوﺗﻌﺎدﻟﯽ ﯾﮏ ﻓﻨﺎوري ﭘﯿﺸﺮﻓﺘﻪ و ﻧﻮﻋﯽ ﻋﻤﻠﯿﺎت ﺣﻔﺎري ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ در آن ﻓﺸﺎر ﺳﯿﺎل ﺣﻔﺎري درون ﭼﺎه ﮐﻤﺘﺮ از ﻓﺸﺎر ﻣﻨﻔﺬي ﺳﺎزﻧﺪ ﻣﯽ ﺑﺎﺷﺪ. اﯾﻦ روش ﺣﻔﺎري ﯾﮏ روش ﺑﻬﯿﻨﻪ در ﺣﻔﺎري اﺳﺖ ﮐﻪ ﺑﺎﻋﺚ ﮐﺎﻫﺶ ﻫﺰﯾﻨﻪ ﻫﺎي ﮐﻠﯽ ﺗﻮﻟﯿﺪ ﻧﻔﺖ، ﮐﺎﻫﺶ ﻣﯿﺰان ﺧﺴﺎرات وارده ﺑﻪ ﻣﺨﺎزن ﻧﻔﺖ و در ﻧﻬﺎﯾﺖ اﻓﺰاﯾﺶ ﺷﺎﺧﺺ ﺑﻬﺮه دﻫﯽ ﭼﺎه ﻫﺎي ﻧﻔﺖ و ﮔﺎز ﻣﯽﺷﻮد. اﯾﻦ ﺗﺤﻘﯿﻖ ﺑﺎ ﻫﺪف ﺑﺪﺳﺖ آوردن ﻣﻌﯿﺎري ﺑﺮاي ﺗﺨﻤﯿﻦ ﺣﺪاﻗﻞ و ﺣﺪاﮐﺜﺮ ﻓﺸﺎر ﻓﺮوﺗﻌﺎدﻟﯽ ﮔﻞ ﺣﻔﺎري ﺑﻪ ﻣﻨﻈﻮر ازدﯾﺎد ﺑﺮداﺷﺖ ﻧﻔﺖ و ﺟﻠﻮﮔﯿﺮي از آﺳﯿﺐ ﺑﻪ ﺳﺎزﻧﺪ در ﻣﺨﺎزن ﮐﺮﺑﻨﺎﺗﻪ اﯾﺮان اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﺑﺮاي رﺳﯿﺪن ﺑﻪ اﯾﻦ ﻫﺪف اﻃﻼﻋﺎت 13 ﭼﺎه از ﻣﯿﺪان ﻫﺎي ﻣﺨﺘﻠﻒ ﻧﻔﺘﯽ اﯾﺮان ﺟﻤﻊ آوري ﺷﺪه و ﺳﭙﺲ ﺑﺎ اﺳﺘﻔﺎده از ﻧﺮم اﻓﺰار FLAC2D ﮐﻪ ﯾﮏ ﺑﺮﻧﺎﻣﻪ ﻋﺪدي ﺑﺮ ﻣﺒﻨﺎي روش ﺗﻔﺎﺿﻞ ﻣﺤﺪود اﺳﺖ، ﺑﻪ ﻣﺪﻟﺴﺎزي ﭼﺎه ﻧﻔﺖ در ﻓﺸﺎرﻫﺎي ﻣﺨﺘﻠﻒ ﮔﻞ ﺣﻔﺎري ﭘﺮداﺧﺘﻪ ﺷﺪه و در ﻧﻬﺎﯾﺖ ﺑﺮاي ﺗﺤﻠﯿﻞ ﭘﺎﯾﺪاري و ﺗﺨﻤﯿﻦ ﺣﺪاﻗﻞ و ﺣﺪاﮐﺜﺮ ﻓﺸﺎر ﻓﺮوﺗﻌﺎدﻟﯽ ﮔﻞ ﺣﻔﺎري، ﺑﻪ روش اﻻﺳﺘﻮﭘﻼﺳﺘﯿﮏ از روش ﺗﻌﯿﯿﻦ ﺳﻄﺢ ﺗﺴﻠﯿﻢ ﻧﺮﻣﺎﻟﯿﺰه Normalized Yielded Zone ﺑﺮاي ﻫﺮ ﭼﺎه ﺑﻪ ﺻﻮرت ﺟﺪاﮔﺎﻧﻪ، ﺑﺎ در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﻓﺸﺎرﻫﺎي ﮔﻞ ﺣﻔﺎري روي ﻧﻤﻮدارNYZA در ﺑﺎزه ﺑﯿﻦ 1=NYZA ﺗﺎ ﻓﺸﺎر ﻣﻨﻔﺬي، ﺣﺪاﻗﻞ و ﺣﺪاﮐﺜﺮ ﻓﺸﺎر ﮔﻞ ﺣﻔﺎري ﺑﻪ ﺗﺮﺗﯿﺐ در 1=NYZA و 0/2=NYZA محاسبه شده و در نهايت رابطه اي به صورت نسبتي از فشار منفذي براي تخمين حداقل و حداكثر فشار فروتعادلي گل حفاري بدست آورده و ارائه شده است. اين رابطه به صورت ضريب يا نسبتي از فشار منفذي بيان شده كه در آن، تنها با داشتن فشار منفذي سازند مي توان حداقل و حداكثر فشار فروتعادلي گل حفاري را به منظور ازدياد برداشت نفت و جلوگيري از آسيب به سازند تخمين زد.

Underbalanced drilling is in fact the best drilling method for oil reservoirs that their pressure has been reduced. This study aimed at obtaining a criterion for estimating the minimum and maximum underbalanced presUnderbalanced drilling is an advanced technology and a drilling operation in which the drilling fluid pressure inside the well is less than the pore pressure of sures of the drilling mud for enhancing oil recovery and preventing damages to the formations in the Iranian carbonate reservoirs. To this end, data on 13 wells in various Iranian oil fields were first collected. The oil wells were simulated at different drilling mud pressures with the help of the finite difference method (FDM)-FLAC2D. The elastoplastic normalized yielded zone area (NYZA) method was used for stability analysis and estimation of the minimum and maximum underbalanced pressures of the drilling mud. The NYZA diagram was plotted separately for each well. Considering the drilling mud pressures on the NYZA diagram in the range of NYZA=1 to the pore pressure, a minimum and maximum drilling mud pressure of NYZA=1 and NYZA=0.2 was calculated, respectively. Eventually, a correlation was proposed as a fraction of the pore pressure to estimate the minimum and maximum underbalanced pressures. This correlation is expressed as a factor or fraction of the pore pressure. The minimum and maximum underbalanced pressures of the drilling mud to enhance oil recovery and prevent damage to the formation can be estimated solely by inserting the pore pressure of the formation in this correlation.