Cerita sedikit tentang Shallow Hazard Assassment

Bismillah, diawali dengan sebuah doa, insya allah di pagi hari ini rasanya ga afdol kalo kita ga sharing sharing tentang ilmu pengetahuan yang sudah kita dapetin, jadi saya mau cerita tentang shallow hazard assasment, kita tahu sendiri kalo shallow itu artinya bawah permukaan dangkal. Biasanya sekitar kedalaman dari 0 – 1500 meter. Kenapa daerah ini dikatakan hazard ? daerah shallow ini dikatakan hazard karena apabila kita ingin drill bawah permukaan mencari minyak atau gas bumi, jika terdapat daerah yang kita cari terdapat daerah yang tekanan fluida formasi > daripada tekanan hidrostatis mud weightnya maka akan terjadi blow out, karena tekanan bergerak dari tekanan tinggi ke tekanan rendah maka pada daerah shallow ini, tekanan tersebut akan menuju permukaan, efeknya bisa bermacam macam, bisa membuat longsor daerah permukaan, apabila pressure tersebut berada tepat di bawah rig yang kita buat, maka dampaknya bisa terlihat pada gambar di bawah ini.

We know and realize shallow hazard assessment use to minimize risk that we can try to avoid it, we use seismic data to interpretation subsurface hazard. 3D seismic data is required to try identify and map these possible hazard, ideally seismic should have been acquired with parameters that focus on the shallow with high revolution ( HR ) 3 D seismic data. If we haven’t, we can use data as order, such as seismic 3D, seismic 2D HR, and seismic 2D.

In this case, we can’t guarantee 100 % that blow out could be happen in our well, because the assessment is done to minimize the risk, but there may still be some hazard that do not show as anomalies in our data seismic, due to seismic data quality limitation and then there is always some uncertainty e.g. seismic acquisition and processing limitation.

When we want to perform shallow gas hazard analysis we required input data that we needed, First, we need 3D seismic data, preferably high resolution, then proposed trajectory of well, then all existing nearby well loaded, then depth to time, or time to depth conversion data, seismic data in time domain and well data in depth domain, and then composite log ( lithologs, mud logs ) and then knowledge / history of previous drilling problems

I enclose work flow for shallow gas hazard below

 

                                                          

                                                                                    

Why we concern with shallow gas is that the main problem shallow gas is that if there is sufficient gas pressure to kick, then there are fewer options to control the well in a shallow open hole ( uncased ) situation, possibility of blowing outside the borehole fracturing the formation where no casing, in the case diverters and BOP may not help. So please drill safely :D