Geomehanički aspekti projektiranja odobalnih bušotina u blizini solnih struktura : diplomski rad

Exploration around the salt bodies has always been challenging for well planning and construction due to associated geological complexity and well-planning uncertainties. With the placement of wells in a deep and complex offshore salt environment, the wellbore stability becomes an all-important element for meeting well construction objectives. The well construction risks associated with instabilities encountered around salt structures can be high to the extent where they drastically influence the well design and delivery costs. To facilitate the planning and drilling of wells in such a challenging and expensive environment, the in-situ conditions around salt bodies must be accurately characterized. In turn, that will enable accurate quantification of formation pressure and fracture gradients, a crucial input for casing design. The standalone approach to well architecture design is often preferred during the planning stage due to its simplicity. However, such an approach may become inadequate once the influence of salt structures on the well design is properly understood. The salt-induced stress perturbations and local geomechanical instabilities found around salt bodies, if underestimated, may incur substantial well construction costs and consequently jeopardize the overall economics of a prospect. Hence, one shall adhere to a holistic approach toward the well architecture design by considering the multiple factors including, but not limited to, geomechanical instabilities, abnormal pore pressures, areas of accelerated creep, and other trajectory-specific drilling problems. In other words, leveraging a multidimensional approach to well architecture design, such that all specific risks peculiar to the offshore salt environment are well understood and evaluated, shall enable operators to capture additional value from the well construction while improving returns, decreasing risks, and enhancing operational safety in Deepwater salt plays.Složenost geoloških struktura u podzemlju i nesigurnosti povezane s istraživanjem ležišta ugljikovodika u blizini solnih naslaga dodatno usložnjavaju proces projektiranja i izrade bušotina u odobalju. Pri projektiranju bušotina u dubljim i složenijim dijelovima odobalja, stabilnost kanala bušotine postaje vrlo važan element u postizanju ciljeva izrade istih. Stupanj nestabilnosti kanala odobalnih bušotina povezanih s bušenjem naslaga soli može utjecati na projektiranje i tehničku izvedbu tako da ugrožava ekonomičnost bušotine. Stoga je važno odrediti deformacije i stanje naprezanja unutar i u neposrednoj blizini naslaga soli, a s ciljem lakšeg planiranja i što efikasnije izrade bušotine. Precizna karakterizacija spomenutih veličina omogućuje točnu procjenu pornog tlaka i gradijenta loma, ključnih parametara za projektiranje zacjevljenja kanala bušotine. S ciljem pojednostavljenja projekta izrade bušotine, utjecaj perturbacija naprezanja i lokalnih geomehaničkih nestabilnosti uzrokovanih dugotrajnim puzanjem soli često je umanjen tijekom procesa planiranja. Posljedično, necjelovit pristup projektiranju može prouzročiti dodatne troškove izrade bušotine u odobalju te, u određenim slučajevima, dovesti u pitanje ekonomsku opravdanost investicije u razradu polja. Stoga je, zbog višestrukog utjecaja solnih struktura na tehničku izvedbu kanala bušotine, vrlo važno holistički pristupiti projektiranju putanje bušotine. Sveobuhvatnim pristupom moguće je konvencionalan pristup planiranju proširiti razmatranjem utjecaja geomehaničkih nestabilnosti, lokalnih perturbacija pornog tlaka, rizika vezanih uz puzanje soli i ostalih problema koji izravno utječu na projektiranje putanje kanala bušotine. Naime, sagledavanjem svih rizika svojstvenih naslagama soli u odobalju, naftno-plinskim kompanijama omogućeno je stvoriti dodanu vrijednost kroz ubrzani povrat ulaganja, smanjenje rizika te povećanje operativne sigurnosti